Re: Generator vs functools.partial?
On Thu, 2012-06-21 at 21:25 +1000, John O'Hagan wrote: Sometimes a function gets called repeatedly with the same expensive argument: def some_func(arg, i): (do_something with arg and i) same_old_arg = big_calculation() for i in lots_of_items: some_func(same_old_arg, i) Another possibility is to refactor this into a callable class. class DoesSomethingWithExpensiveData(object): def __init__(self, arg): self.arg = arg def __call__(self, operand): return sum([self.arg, operand]) func = DoesSomethingWithExpensiveData(big_calculation()): for thing in a_bunch_of_things: print func(thing) Or you can write a function factory: def get_func(arg): def inner(operand): return sum([arg, operand]) return inner func = get_func(big_calculation()) for thing in a_bunch_of_things: print func(thing) A simple case like that looks OK, but it can get messy when groups of arguments are passed between functions, especially if the arguments are used by functions called within the functions they are passed to (by other functions!). Maybe that's a code smell, but it can be cleaned up with: import functools some_func = functools.partial(some_func, big_calculation()) for i in lots_of_items: some_func(i) But what about a generator? def some_func(): arg = big_calculation() while 1: i = yield (do_something with arg and i) some_gen = some_func() some_gen.send(None) for i in lots_of_items: some_gen.send(i) I like this because it encapsulates the calculation of the arguments inside the function that is using them without repeating it, and there are no restrictions on argument order like partial. But sending None is annoying. :) Old news? Thoughts, criticisms, theories? -- John -- http://mail.python.org/mailman/listinfo/python-list
Re: Academic citation of Python
That's a rather vague question. What do you want to cite about python? If you're just mentioning python, that shouldn't warrant a citation, though a parenthetical note linking to python.org might be useful. The standard documentation should be acceptable, or possibly a link to the source code at a given revision. Cheers, Cliff On Sat, 2012-06-16 at 13:24 +1000, Mark Livingstone wrote: Hello! I wish to properly cite Python in an academic paper I am writing. Is there a preferred document etc to cite? Thanks in advance, MArkL -- http://mail.python.org/mailman/listinfo/python-list
Re: Interprocess comunication
On Thu, 2012-06-07 at 16:04 +, Julio Sergio wrote: Up to this point it worked as expected. However, when I tryied with the methods that write and read several lines, apparently the process got stalled: - fi.writelines([uno\n,dos\n,tres\n]) - fi.flush() - s = fo.readlines() . . . readlines() reads all the lines from the filehandle, but the filehandle hasn't signalled that it is done writing lines, so fo is waiting until fi is complete. You either need to keep reading one line at a time, and manually release control when there's nothing more to read, or you need to do an fi.close() before you try to use fo.readlines(). -- http://mail.python.org/mailman/listinfo/python-list
Re: Interprocess comunication
It is for reading all the lines from a complete file. If the file is still being written to, it doesn't have an end yet. File objects do many things besides RPC. Also, there are instances where all you want to do is block until the file is done, and then get all the content. readlines will do that, too. On Thu, 2012-06-07 at 16:39 +, Julio Sergio wrote: MRAB python at mrabarnett.plus.com writes: I believe it's waiting for the end of the input, i.e. for the pipe to close. Have you tried calling fo.readline() 3 times instead? yeah! It worked!... A question remains: what is then the purpose of fo.readlines(...)? Thanks, --Sergio -- http://mail.python.org/mailman/listinfo/python-list
Re: I look for a package to make some simple console form
You might look into formencode. It basically takes the philosophy that a form is nothing more and nothing less than an interface between user input and python data. It doesn't make assumptions about how you present the form to the user. It just handles validation and conversion of that data into useful python objects, and from python objects to displayable values. http://www.formencode.org/en/latest/Validator.html Might be what you're looking for. Cheers, Cliff On Mon, 2012-04-02 at 14:55 +0200, Stéphane Klein wrote: Hi, I look for a package to make some console form. It's a standard stuff, I think there are a package to do that. Example : What is your name ? Select your lang [EN, FR, DE…] ? Do you want … [Y, N] ? Type of field : * textline * select choice * boolean question Thank for your help, Stéphane -- Stéphane Klein steph...@harobed.org blog: http://stephane-klein.info Twitter: http://twitter.com/klein_stephane pro: http://www.is-webdesign.com -- http://mail.python.org/mailman/listinfo/python-list
Re: help needed to understand an error message.
So the problem is that python doesn't know what you're trying to do. It doesn't know that you meant to say print. When the parser is looking at the word Print, it assumes you are referencing an object named Print, which is completely legal. It's only once you've created the next token, a string literal, that the parser discovers the error: you can't have a string literal following a variable. *You* think your error is that you misspelled print. The parser thinks your error is trying to put a string literal next to a variable. Cheers, Cliff On Mon, 2012-03-26 at 18:22 +0530, Aloke Ghosh wrote: Hi, I am learning Python and do not have programming experience. I was following an exercise from http://learnpythonthehardway.org/book/ex2.html and made a mistake in entry : PrintI like typing this. and got the following error message: In [2]: PrintI like typing this. File ipython console, line 1 PrintI like typing this. ^ SyntaxError: invalid syntax I feel the error is in Capital P in print . However the error indicated with ^ hints at quote at the end of the line. Can any one please help me understand this. -- A.K.Ghosh -- http://mail.python.org/mailman/listinfo/python-list
Re: Is there any difference between print 3 and print '3' in Python ?
As others have pointed out, the output is the same, because the result of converting an integer to a string is the string of that integer. However, other numeric literals might not do what you want, due to the fact that they are converted to an internal numeric representation, then converted back to a string in a canonical format. print 3, '3' 3 3 print 3.00, '3.00' 3.0 3.00 print 0x3, '0x3' 3 0x3 print 03, '03' 3 03 print 3e0, '3e0' 3.0 3e0 You might think that the take away message is to use the string representation, since it prints what you tell it to print. However, if you use a number, you can specify the output formatting with more fine-grained control, and even exert that control on calculated number: print '%0.2f' % (3,) 3.00 print '%0.2f' % (2 + 1) 3.00 This is better because you can't perform math on a string: print '2' + '1' 21 print '2.00' + '1.00' 2.001.00 print '2 + 1' 2 + 1 So in general, you should use numbers, and then format them using standard string formatting operations when you want to print them. There's more information on how to do formatting here: http://docs.python.org/library/stdtypes.html#string-formatting Cheers, Cliff On Mon, 2012-03-26 at 04:45 -0700, redstone-c...@163.com wrote: I know the print statement produces the same result when both of these two instructions are executed ,I just want to know Is there any difference between print 3 and print '3' in Python ? -- http://mail.python.org/mailman/listinfo/python-list
Re: Python classes: Simplify?
The issue of explicitly naming a self parameter has been discussed in
depth on a number of occasions. I recommend a google search for python
implicit self for some of the reasons why it exists. Here's what Guido
has to say about it:
http://neopythonic.blogspot.com/2008/10/why-explicit-self-has-to-stay.html
Cheers,
Cliff
On Thu, 2012-03-22 at 13:15 +, Andrea Crotti wrote:
On 03/22/2012 10:51 AM, Steven Lehar wrote:
It seems to me that the Python class system is needlessly confusing.
Am I missing something?
For example in the class Complex given in the documentation
class Complex:
def __init__(self, realpart, imagpart):
self.r = realpart
self.i = imagpart
x = Complex(3.0, -4.5)
I initially found it profoundly confusing that __init__( ) calls for
3 arguments, but you call Complex( ) with 2. Furthermore, why not
call the initialization function after the class name as is done in
other languages? Isn't that the simplest conceptually? Demonstrating
with the above example:
class Complex:
def Complex(realpart, imagpart):
Complex.r = realpart
Complex.i = imagpart
x = Complex(3.0, -4.5)
Is there a good reason why classes cannot be defined that way?
(Besides the problem of backward-compatibility)
Some time ago I saw some nasty hack that allowed you to drop the self
in the method declaration,
using some crazy metaclass trick, but that's really not a good idea ;)
I agree that is counter-intuitive but just set your editor to do that
for you and you will be fine..
in my emacs
- s TAB - self
- . TAB - self.
- m TAB - def ${1:method}(self$2):
$0
so I never actually write the self..
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Re: List comprehension/genexp inconsistency.
Thanks, Ian. That does seem to explain it. The inner loop doesn't have access to the class's name space, and of course you can't fix it by referencing Foo.y explicitly, because the class isn't fully defined yet. Ultimately, we realized that the dict should be created in the __init__ method, so that it gets the appropriate values of the foo and bar attributes if the class is subclassed, which obviates the problem, but it's a fascinating peek into python internals. It looks like this is explained in the section of the pep entitled Early Binding versus Late Binding http://www.python.org/dev/peps/pep-0289/#early-binding-versus-late-binding Cheers, Cliff On Tue, 2012-03-20 at 16:50 -0600, Ian Kelly wrote: On Tue, Mar 20, 2012 at 3:16 PM, Dennis Lee Bieber wlfr...@ix.netcom.com wrote: On Tue, 20 Mar 2012 16:23:22 -0400, J. Cliff Dyer j...@sdf.lonestar.org declaimed the following in gmane.comp.python.general: When trying to create a class with a dual-loop generator expression in a class definition, there is a strange scoping issue where the inner variable is not found, (but the outer loop variable is found), while a list comprehension has no problem finding both variables. Read http://www.python.org/dev/peps/pep-0289/ -- in particular, look for the word leak No, this has nothing to do with the loop variable leaking. It appears to have to do with the fact that the variables and the generator expression are inside a class block. I think that it's related to the reason that this doesn't work: class Foo(object): x = 42 def foo(): print(x) foo() In this case, x is not a local variable of foo, nor is it a global. In order for foo to access x, it would have to be a closure -- but Python can't make it a closure in this case, because the variable it accesses is (or rather, will become) a class attribute, not a local variable of a function that can be stored in a cell. Instead, the compiler just makes it a global reference in the hope that such a global will actually be defined when the code is run. For that reason, what surprises me about Cliff's example is that a generator expression works at all in that context. It seems to work as long as it contains only one loop, but not if it contains two. To find out why, I tried disassembling one: class Foo(object): ... x = 42 ... y = 12 ... g = (a+b for a in range(x) for b in range(y)) ... dis.dis(Foo.g.gi_code) 4 0 LOAD_FAST0 (.0) 3 FOR_ITER34 (to 40) 6 STORE_FAST 1 (a) 9 LOAD_GLOBAL 0 (range) 12 LOAD_GLOBAL 1 (y) 15 CALL_FUNCTION1 18 GET_ITER 19 FOR_ITER15 (to 37) 22 STORE_FAST 2 (b) 25 LOAD_FAST1 (a) 28 LOAD_FAST2 (b) 31 BINARY_ADD 32 YIELD_VALUE 33 POP_TOP 34 JUMP_ABSOLUTE 19 37 JUMP_ABSOLUTE3 40 LOAD_CONST 0 (None) 43 RETURN_VALUE So that explains it. Notice that x is never actually accessed in that disassembly; only y is. It turns out that the first iterator [range(x)] is actually created before the generator ever starts executing, and is stored as an anonymous local variable on the generator's stack frame -- so it's created in the class scope, not in the generator scope. The second iterator, however, is recreated on every iteration of the first iterator, so it can't be pre-built in that manner. It does get created in the generator scope, and when that happens it blows up because it can't find the variable, just like the function example above. Cheers, Ian -- http://mail.python.org/mailman/listinfo/python-list
Re: Best way to disconnect from ldap?
Write a context manager.
Then you just do
with MyLDAPWrapper() as ldap
ldap.this()
ldap.that()
and when you leave the scope of the with statement, your ldap __exit__
method will get called regardless of how you left.
Cheers,
Cliff
On Wed, 2012-03-21 at 19:30 +, John Gordon wrote:
I'm writing an application that interacts with ldap, and I'm looking
for advice on how to handle the connection. Specifically, how to
close the ldap connection when the application is done.
I wrote a class to wrap an LDAP connection, similar to this:LDAP
import ldap
import ConfigParser
class MyLDAPWrapper(object):
def __init__(self):
config = ConfigParser.SafeConfigParser()
config.read('sample.conf')
uri = config.get('LDAP', 'uri')
user = config.get('LDAP', 'user')
password = config.get('LDAP', 'password')
self.ldapClient = ldap.initialize(uri)
self.ldapClient.simple_bind_s(user, password)
My question is this: what is the best way to ensure the ldap connection
gets closed when it should? I could write an explicit close() method,
but that seems a bit messy; there would end up being lots of calls to
close() scattered around in my code (primarily inside exception handlers.)
Or I could write a __del__ method:
def __del__(self):
self.ldapClient.unbind_s()
This seems like a much cleaner solution, as I don't ever have to worry
about closing the connection; it gets done automatically.
I haven't ever used __del__ before. Are there any 'gotchas' I need to
worry about?
Thanks!
--
John Gordon A is for Amy, who fell down the stairs
gor...@panix.com B is for Basil, assaulted by bears
-- Edward Gorey, The Gashlycrumb Tinies
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List comprehension/genexp inconsistency.
One of my coworkers just stumbled across an interesting issue. I'm hoping someone here can explain why it's happening. When trying to create a class with a dual-loop generator expression in a class definition, there is a strange scoping issue where the inner variable is not found, (but the outer loop variable is found), while a list comprehension has no problem finding both variables. Demonstration: class Spam: ... foo, bar = 4, 4 ... baz = dict(((x, y), x+y) for x in range(foo) for y in range(bar)) ... Traceback (most recent call last): File stdin, line 1, in module File stdin, line 3, in Spam File stdin, line 3, in genexpr NameError: global name 'bar' is not defined class Eggs(object): ... foo, bar = 4, 4 ... baz = dict([((x, y), x+y) for x in range(foo) for y in range(bar)]) ... This was discovered in python 2.6. In python 3.2, both versions fail with the same NameError. Obviously, this is easy enough to work around. I'm curious though: What's going on under the hood to cause the nested generator expression to fail while the list comprehension succeeds? Cheers, Cliff -- http://mail.python.org/mailman/listinfo/python-list
Re: super() woes (n00b)
On Thu, 2010-06-17 at 16:36 +, Deadly Dirk wrote: I cannot get right the super() function: Python 3.1.1+ (r311:74480, Nov 2 2009, 14:49:22) [GCC 4.4.1] on linux2 Type copyright, credits or license() for more information. No Subprocess class P: def __init__(__class__,self): print(I am a member of class P) class C(P): def __init__(self): super().__init__(self) print(I am a member of class C) class P: def __init__(self): print(I am a member of class P) class C(P): def __init__(self): super().__init__(self) print(I am a member of class C) x=C() That is more or less the text from the Quick Python Book. What am I doing wrong? super gives you an instantiated version of the super class, which means that you don't have to explicitly send self to any methods you call on it. So use `super().__init__()` instead. -- The missionaries go forth to Christianize the savages - as if the savages weren't dangerous enough already. -- http://mail.python.org/mailman/listinfo/python-list
Re: optional optional args vs optional positional options
+1 Options are options, arguments are arguments. An optional argument is not an option. It is an argument that can be left out. On Wed, 2010-06-02 at 12:42 +0200, Antoine Pitrou wrote: On Wed, 2 Jun 2010 01:49:18 -0700 (PDT) Michele Simionato michele.simion...@gmail.com wrote: Notice that optparse is basically useless in the use case Tim is considering (positional arguments) since it only manages options. By the way, could you stop naming these optional arguments, since positional arguments can be optional as well? It is confusing :) Thanks Antoine. -- http://mail.python.org/mailman/listinfo/python-list
Re: how to preserve hex value
On Wed, 2010-05-19 at 11:38 -0700, Back9 wrote:
Hi,
When converting a hex value, I'd like to preserve the decimal
position.
For example, 0x0A is converted to 0A not just A in string.
How do I do this?
TIA
I'm not sure I understand what your use case is, but generally speaking,
it is better to treat hex values as integers (which they are) than as
string (which they are not). 0x0a is an integer value of ten. There is
no change of decimal position gained by prepending a zero digit. It
means exactly the same thing. If you know how large a chunk is, you can
multiply (or bit-shift) and add to get the behavior you're looking for.
def concat(byte1, byte2):
return (byte1 8) + byte2
hex(concat(0x43, 0x0a))
0x430a
One common use case is when using hex notation to represent sequences of
bytes. In this case, you may want to work with a byte string instead.
To concatenate your numbers this way, convert each number to a byte
using chr(x) (Python 2.x)
To print it as hex, do something like this:
def bytestring_to_hex(s):
return '0x + ''.join('%02x' % ord(x) for x in s)
However, if you need an arbitrary number of zeros preserved, you're out
of luck. They are semantically meaningless in python. (Is semantically
meaningless redundant?)
Cheers,
Cliff
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Re: Regular expression
Don't use regular expressions for that.
s = '0x340x5A0x9B0xBA'
return '0x' + ''.join(s.split('0x'))
On Tue, 2010-05-18 at 06:48 -0700, Back9 wrote:
Hi,
I have a string like this:
0x340x5A0x9B0xBA
I want to extract 0x from the string but the first one.
How I can use re for this case?
The string size will vary.
TIA
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Re: unittest not being run
My guess is you mixed tabs and spaces. One tab is always treated by the
python interpreter as being equal to eight spaces, which is two
indentation levels in your code.
Though if it were exactly as you show it, you'd be getting a syntax
error, because even there, it looks like the indentation of your `def
test_T1(self):` line is off by one column, relative to pass, and by
three columns relative to the other methods.
Cheers,
Cliff
On Mon, 2010-05-10 at 13:38 +0100, John Maclean wrote:
hi,
can some one explain why the __first__ test is not being run?
#!/usr/bin/env python
import unittest # {{{
class T1TestCase(unittest.TestCase):
def setUp(self):
pass # can we use global variables here?
def tearDown(self):
pass # garbage collection
def test_T1(self):
'''this test aint loading'''
self.assertEquals(1, 0)
def test_T2(self): ## test method names begin 'test*'
self.assertEquals((1 + 2), 3)
self.assertEquals(0 + 1, 1)
def test_T3(self):
self.assertEquals((0 * 10), 0)
self.assertEquals((5 * 8), 40)
# the output is better. prints each test and ok or fail
suite = unittest.TestLoader().loadTestsFromTestCase(T1TestCase)
unittest.TextTestRunner(verbosity=2).run(suite) # }}}
''' halp!
the first test ain't loading...
python blaht.py
test_T2 (__main__.T1TestCase) ... ok
test_T3 (__main__.T1TestCase) ... ok
--
Ran 2 tests in 0.000s
OK
'''
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Re: Frustration debugging serial code
On Fri, 2010-05-07 at 15:36 -0400, William R. Wing wrote: Maybe I should have been more explicit. The first line in the Python file is: #!/usr/bin/env Python (alternatively #!/usr/bin/Python - same results either way). python should be lowercased when referring to the name of the executable. Unix filesystems are, of course, case sensitive. -- http://mail.python.org/mailman/listinfo/python-list
Re: Frustration debugging serial code
On Fri, 2010-05-07 at 15:36 -0400, William R. Wing wrote: Maybe I should have been more explicit. The first line in the Python file is: #!/usr/bin/env Python (alternatively #!/usr/bin/Python - same results either way). python should be lowercased when referring to the name of the executable. Unix filesystems are, of course, case sensitive. -- http://mail.python.org/mailman/listinfo/python-list
Re: Python dot-equals (syntax proposal)
That's kind of a nifty idea. However, python is currently under a syntax moratorium. No syntax changes will be accepted for at least 24 months starting from the release date of Python 3.1. See more details here: http://www.python.org/dev/peps/pep-3003/ Cheers, Cliff On Fri, 2010-04-30 at 09:04 -0700, Jabapyth wrote: At least a few times a day I wish python had the following shortcut syntax: vbl.=func(args) this would be equivalent to vbl = vbl.func(args) example: foo = Hello world foo.=split( ) print foo # ['Hello', 'world'] and I guess you could generalize this to vbl.=[some text] # vbl = vbl.[some text] e.g. temp.=children[0] # temp = temp.children[0] thoughts? -- http://mail.python.org/mailman/listinfo/python-list
Re: how to select column
It depends on what you mean by a column. I assume your data is more
complex than what you've shown us.
If your data is really single words separated by spaces, you can do:
for line in open('file'):
columns = line.split()
return columns[0], columns[3]
If your columns can have spaces within them, or are separated in other
ways, you'll need something else.
Cheers,
Cliff
On Mon, 2010-04-26 at 14:50 +, mannu jha wrote:
Dear all,
I am new in python, can anyone help me that how can I select two
column out of 6 column from a file.
For example if I have file like:
a1 a2 a3 a4 a5 a6
b1 b2 b3 b4 b5 b6
c1 c2 c3 c4 c5 c6
d1 d2 d3 d4 d5 d6
and I want output like:
a1 a4
b1 b4
c1 c4
d1 d4
then how to do
Thanks
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Re: Difficulty w/json keys
You need to know what your input data actually looks like, and the best
thing for that is a little bit of formatting. I bet you can figure out
the problem yourself, once you see the structure of your data more
clearly. I've reformatted the JSON for you to help out.
On Fri, 2010-04-23 at 07:20 -0700, Red wrote:
-- Two Sample Twitter lines -
{
text:tech managers what size for your teams? better to have 10-20
ppl per manager or 2-5 and have the managers be more hands
on?,
in_reply_to_user_id:null,
coordinates:null,
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created_at:Thu Apr 22 17:35:42 + 2010,
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source:a href=\http://twitterfeed.com\; rel=\nofollow
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user: {
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time_zone:Eastern Time (US Canada),
created_at:Tue Oct 27 19:50:51 + 2009,
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profile_link_color:ff,
description:I write code and talk to people.,
lang:en,
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location:Near the water.,
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{
delete: {
status:{
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Re: question about list extension
On Sat, 2010-04-17 at 00:37 +1000, Lie Ryan wrote: On 04/16/10 23:41, J wrote: So, what I'm curious about, is there a list comprehension or other means to reduce that to a single line? from itertools import chain def printout(*info): print '\n'.join(map(str, chain(*info))) or using generator comprehension from itertools import chain def printout(*info): print '\n'.join(str(x) for x in chain(*info)) It's even easier if you don't need to modify lista. print lista + listb -- http://mail.python.org/mailman/listinfo/python-list
Re: Globally override built-in print function?
On Fri, 2010-04-16 at 09:50 -0700, Dave W. wrote: old_print = __builtins__.print __builtins__.print = printhook yield __builtins__.print = old_print I'm pretty sure this is semantically equivalent to my original code, but I gave it a try anyway. Not at all. Declaring global print then assigning to print simply changes what the module's print variable refers to. Other modules are unaffected. Global variables aren't truly global; they are actually local to the module. You need to replace it in the __builtins__ because that's where everyone else gets it. FWIW, it doesn't work, either. :-} Right. Lie answered why. I didn't pay attention and thought you were already using Python 3. Thanks, Robert and Lie for the considered and informative responses. Getting feedback like this from people who really understand Python's internals is invaluable. Sounds like redirecting stdout/stderr is the way to go. (Especially given that they're not the 'real' stdout/stderr---that was news to me!) [xref Suppress output to stdout/stderr in InteractiveInterpreter] It's good to remember that names in python are just names. The objects that have the names sys.stdout and sys.stderr are the real deal, but when you assign a file object to them, you are not actually redirecting anything. You are assigning a name (sys.stdout) to a different file object. The old object still points to STDOUT, but sys.stdout no longer refers to that object as long as your assignment remains in scope. -- http://mail.python.org/mailman/listinfo/python-list
Re: Urllib2 urlopen and read - difference
On Thu, 2010-04-15 at 11:25 -0700, koranthala wrote:
Hi,
Suppose I am doing the following:
req = urllib2.urlopen('http://www.python.org')
data = req.read()
When is the actual data received? is it done by the first line? or
is it done only when req.read() is used?
My understanding is that when urlopen is done itself, we would have
received all the data, and req.read() just reads it from the file
descriptor.
But, when I read the source code of pylot, it mentioned the
following:
resp = opener.open(request) # this sends the HTTP request
and returns as soon as it is done connecting and sending
connect_end_time = self.default_timer()
content = resp.read()
req_end_time = self.default_timer()
Here, it seems to suggest that the data is received only after you do
resp.read(), which made me all confused.
If someone could help me out, it would be much helpful.
My understanding (please correct me if I'm wrong), is that when you call
open, you send a request to the server, and get a response object back.
The server immediately begins sending data (you can't control when they
send it, once you've requested it). When you call read() on your
response object, it reads all the data it has already received, and if
that amount of data isn't sufficient to handle your read call, it blocks
until it has enough.
So your opener returns as soon as the request is sent, and read() blocks
if it doesn't have enough data to handle your request.
Cheers,
Cliff
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Re: Urllib2 urlopen and read - difference
On Thu, 2010-04-15 at 11:25 -0700, koranthala wrote:
Hi,
Suppose I am doing the following:
req = urllib2.urlopen('http://www.python.org')
data = req.read()
When is the actual data received? is it done by the first line? or
is it done only when req.read() is used?
My understanding is that when urlopen is done itself, we would have
received all the data, and req.read() just reads it from the file
descriptor.
But, when I read the source code of pylot, it mentioned the
following:
resp = opener.open(request) # this sends the HTTP request
and returns as soon as it is done connecting and sending
connect_end_time = self.default_timer()
content = resp.read()
req_end_time = self.default_timer()
Here, it seems to suggest that the data is received only after you do
resp.read(), which made me all confused.
If someone could help me out, it would be much helpful.
My understanding (please correct me if I'm wrong), is that when you call
open, you send a request to the server, and get a response object back.
The server immediately begins sending data (you can't control when they
send it, once you've requested it). When you call read() on your
response object, it reads all the data it has already received, and if
that amount of data isn't sufficient to handle your read call, it blocks
until it has enough.
So your opener returns as soon as the request is sent, and read() blocks
if it doesn't have enough data to handle your request.
Cheers,
Cliff
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Re: Unit testing errors (testing the platform module)
On Wed, 2010-04-14 at 15:51 +0100, john maclean wrote: self.assertEqual(platform.__builtins__.__class__, dict, platform.__class__ supposed to be dict) self.assertEqual(platform.__name__, 'platform' ) The preferred spelling for: platform.__builtins__.__class__ would be type(platform.__builtins__) It's shorter and easier to read, but essentially says the same thing. You can also use it on integer literals, which you can't do with your syntax: type(1) type 'int' 1.__class__ ... SyntaxError: invalid syntax Admittedly, this is a trivial benefit. If you're using a literal, you already know what type you're dealing with. Cheers, Cliff -- http://mail.python.org/mailman/listinfo/python-list
Re: Unit testing errors (testing the platform module)
The problem is that the class of platform.__builtins__ is a dict, not a string containing the text type 'dict'. Try replacing line 16 with this: self.assertEqual(type(platform.__builtins__), dict) Cheers, Cliff On Tue, 2010-04-13 at 15:01 +0100, John Maclean wrote: I normally use languages unit testing framework to get a better understanding of how a language works. Right now I want to grok the platform module; 1 #!/usr/bin/env python 2 '''a pythonic factor''' 3 import unittest 4 import platform 5 6 class TestPyfactorTestCase(unittest.TestCase): 7 def setUp(self): 8 '''setting up stuff''' 13 14 def testplatformbuiltins(self): 15 '''platform.__builtins__.blah ''' 16 self.assertEquals(platform.__builtins__.__class__, type 'd ict') 17 18 19 def tearDown(self): 20 print 'cleaning stuff up' 21 22 if __name__ == __main__: 23 unittest.main() Is there an error in my syntax? Why is my test failing? Line 16. python stfu/testing/test_pyfactor.py Fcleaning stuff up == FAIL: platform.__builtins__.blah -- Traceback (most recent call last): File stfu/testing/test_pyfactor.py, line 16, in testplatformbuiltins self.assertEquals(platform.__builtins__.__class__, type 'dict') AssertionError: type 'dict' != type 'dict' -- Ran 1 test in 0.000s FAILED (failures=1) -- John Maclean MSc. (DIC) Bsc. (Hons),Core Linux Systems Engineering,07739 171 531 -- http://mail.python.org/mailman/listinfo/python-list
Re: New to Python
On Wed, 2010-02-10 at 13:18 -0800, Stephen Hansen wrote:
The original code:
s = f.readline()
if 'mystring' in s: print 'foundit'
if 'mystring' not in s: print 'not found'
if 'mystring' in s:
print 'processing'
... will only work on Python 2.x, as print is being used as a
statement. If you change print to a function, that code will work in
either Python 2.x or Python 3.x.
However, in both CPython and IronPython, the above is provably correct
code. It works fine: with those five lines alone, you are guaranteed
to get 'foundit' followed by 'processing' if mystring is in s. With
those five lines alone, you must get that result. If you aren't, then
there's something else going on before or after-- and its not about
IronPython vs CPython. To help diagnose what's wrong, copy and paste
-real- results from a command prompt or interpreter when you run it,
providing complete code. Something else is going wrong, you're looking
in the wrong place to find the solution.
One other assumption that you are making is that f is a file-like object
that supports a reasonalbe readline function.
Quin: can you Ctrl-C, Ctrl-V the following code into a python file, by
itself, and run it to reproduce your problem?
from StringIO import StringIO
f = StringIO('This string contains mystring')
s = f.readline()
if 'mystring' in s: print 'foundit'
if 'mystring' not in s: print 'not found'
if 'mystring' in s:
print 'processing'
# Should print:
# foundit
# processing
f = StringIO('This string does not contain MyStRiNg')
s = f.readline()
if 'mystring' in s: print 'foundit'
if 'mystring' not in s: print 'not found'
if 'mystring' in s:
print 'processing'
# Should print:
# not found
And please, humor me and copy and paste the exact results as returned by
your IronPython interpreter.
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Re: Another Screwy Problem
On Sat, 2010-01-09 at 07:59 -0500, Victor Subervi wrote: On Fri, Jan 8, 2010 at 4:44 PM, J. Clifford Dyer j...@sdf.lonestar.org wrote: Victor Subervi wrote: Hi; I have this line of code: sql = 'select Name, Price from %sPackages where ID=%s;' % (store, pid) which prints to this: select Name, Price from productsPackages where ID=1; which when I enter it into the MySQL interpreter gives me this: mysql select Name, Price from productsPackages where ID=1; +--++ | Name | Price | +--++ | pkg | 123.45 | +--++ 1 row in set (0.00 sec) exactly what I expect. However, in my script for some reason it returns this: ((1,),) First, got your other email. I thought I had executed the statement. Oops. Works fine now. Sorry. First, never use string formatting to pass parameters to your database. Read the MySQLdb documentation (or sqlite, or psycopg2) documentation for reasons why, and how to do it right. The only thing I found, which collaborates with something someone else taught me on this list about entering binary data, is that one must pass the parameters in the execute statement. Is that what you mean? If so, I find that for all purposes thus far other than binary data, the way I've been doing it seems to work just fine. I would prefer to keep doing it that way, because I find putting a print statement between the sql= line and the execute statement gives me a good opportunity to review the sql statement and catch errors. Is this not good practice? Thanks. beno This is a horrendous practice. You leave yourself vulnerable not only to attacks, but to simple absent-mindedness as well. Using parameters in your execute statement will handle all necessary quoting for you, which eliminates the possibility of a bad query sneaking in. For more information, as I mentioned, look up SQL injection. Also, read this: http://xkcd.com/327/ Cheers, Cliff -- http://mail.python.org/mailman/listinfo/python-list
Re: Help with cumulative sum
If I gave you a list of numbers, could you come up with a summifier function that returns another list of numbers that are a cumulative sum? You've got the information in place to create a file def summifier(nums): Returns a list of numbers that are the running sum totals of nums # ??? list_of_numbers = [1, 24, 34, 28, 4, 1] cumulative_sum = summifier(list_of_numbers) assert(cumulative_sum == [1, 25, 59, 87, 91, 92]) If you can come up with the summifier function, you're all set. I gotta say, though, this smells like homework. Cheers, Cliff On Tue, 2009-09-08 at 12:29 -0700, Maggie wrote: Building on the code that I posted in one of the previous posts.. I need to find a cumulative sum of the file of the times in the test file: here is the code i have: #!/usr/bin/python import os.path #name of output file filename = OUTPUT.txt #open the file test = open (test.txt, rU) #read in all the data into a list readData = test.readlines() count = 0 FILE = open(filename, w) for item in readData: count = count + 1 tmp_string = str(count) + '' + item print FILE, tmp_string, else: print 'The loop is finito' - my test file is this 23 241 34234 83 123 and I need to find a CUMULATIVE sum (or the running sum)...what would be the best way to go about that given the code i already have? thank you all! -- http://mail.python.org/mailman/listinfo/python-list
Re: Numeric literals in other than base 10 - was Annoying octal notation
I had an objection to using spaces in numeric literals last time around and it still stands, and it still stands in the new one. What happens if you use a literal like 0x10f 304? Is 304 treated as decimal or hexadecimal? It's not clear how you would begin to combine it The way string concatenation works, it takes two independent string literals, and combines them. If you specify r'\n' 'abc\n', the first half is treated independently as a raw string, and the second half is treated as a normal string. The result is '\\nabc\n'. With numeric literals, this behavior doesn't even make sense. How do you concatenate hex 10f with decimal 304? I suppose you could multiply 0x10f by 1000, and add them, but this probably wouldn't fit any practical usecase. Alternatively, you could raise an exception, and require the user to use numeric literals of the same type, like 0x10f 0x304, but then you lose any readability benefit you might have gained by dropping the _ to begin with. If, on the other hand, you want to combine the tokens before processing their independent meanings, which makes the most intuitive sense, well, in that case we're no longer talking about an operation analogous to string contcatenation. We're talking about integers no longer being simple tokens that can be assigned a value. I'm not familiar with the code that makes all this happen in C Python (or any other implementation for that matter), but it seems like it extends the complexity of the parser unnecessarily. I'm concerned that the benefit in readability will be outweighed by the burden it places on the parser, and the cognitive burden on the programmer of knowing what to expect when using non-decimal numeric literals. For that reason, I'm a -1 on using a space in numeric literals, but +1 on using some other separator, and an _, in spite of its slight awkwardness in typing, seems like a good idea. If someone with a solid understanding of the python parser could chime in that this wouldn't cause as much friction as I think, and explain a clean, elegant implementation for this, many of my concerns would be alleviated, and I would change my -1 to a -0. Cheers, Cliff On Mon, 2009-08-24 at 00:01 +1000, Ben Finney wrote: garabik-news-2005...@kassiopeia.juls.savba.sk writes: Why not just use the space? 123 000 looks better than 123_000, and is not syntactically ambiguous (at least in python). And as it already works for string literals, it could be applied to numbers, too… +1 to all this. I think this discussion was had many months ago, but can't recall how it ended back then. -- \ “Only the educated are free.” —Epictetus, _Discourses_ | `\ | _o__) | Ben Finney -- http://mail.python.org/mailman/listinfo/python-list
Re: How to create functors?
On Wed, 2009-08-19 at 15:56 +0200, Bruno Desthuilliers wrote:
Terry Reedy a écrit :
Robert Dailey wrote:
I'm using Python 2.6. And using the legacy syntax in the lambda does
not work either. I want to avoid using a def if possible. Thanks.
In Python, writing
name = lambda arg: expr
instead of
def name(arg): return expr
is all negative and no positive and should be avoided.
Except that def is a statement, and as such can't be used as a named
params when calling a function expecting a callback, ie:
vroom = some_dead('parrot', name=lambda arg: exp)
(notice the 'name = lambda arg: exp' ?-)
Which offers no added functionality over:
def name_func(arg):
return exp
vroom = some_dead('parrot', name=name_func)
except for confusion in debugging. :) (See other excessively long
threads on lambda for further discussion of the debugging headaches
caused by lambdas.
Ok, nitpicking. Me ---[]
g
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Re: variable scoping question.
On Mon, 2009-08-10 at 08:46 -0700, Cornelius Keller wrote: On 10 Aug., 17:12, Diez B. Roggisch de...@nospam.web.de wrote: Cornelius Keller wrote: [snip] http://effbot.org/zone/default-values.htm Diez Ok thank you. I' understand now why. I still think this is very confusing, because default values don't behave like most people would expect without reading the docs. - Cornelius You are correct. This is confusing at first blush. The important thing to remember is: *don't do that.* Learn the pythonic workaround of using None in your parameters whenever you want a default empty list, and don't let it bother you too much. Overall, python is a remarkably well designed language. This is one of the relatively rare warts that crept in because it enables a broader cleanliness of design. Cheers, Cliff -- http://mail.python.org/mailman/listinfo/python-list
Re: dictionary help
On Mon, 2009-08-10 at 22:11 -0400, Krishna Pacifici wrote:
Hi,
kind of a newbie here, but I have two questions that are probably
pretty simple.
1. I need to get rid of duplicate values that are associated with
different keys in a dictionary. For example I have the following
code.
s={}
s[0]=[10,2,3]
s[10]=[22,23,24]
s[20]=[45,5]
s[30]=[2,4]
s[40]=[6,7,8]
Now I want to be able to loop through the primary keys and get rid of
duplicates (both in keys and values) so that I would have either a new
dictionary or the same dictionary but with the following values:
s[0]=[3]
s[10]=[22,23,24]
s[20]=[45,5]
s[30]=[2,4]
s[40]=[6,7,8]
It doesn't matter which value gets removed as long as there is only
one remaining, so in this example it doesn't matter that 2 got removed
from s[0] or from s[30] as long as there is only one 2 in the
dictionary.
So if the number is a key, you want to keep the key, and delete all
matching values, and if the number is not a key, you want to keep one
(any one) instance of that number? I'm not sure that what you are
looking for is best represented by a dict. You might want to consider
creating your own class and overriding __getitem__.
2. I need to be able to loop over the values in the dictionary when
there are multiple values assigned to each key like above and assign
new values to those values. Taking the above example I would want to
assign a new value so that when you called s[0] it would equal [3,4]
say if 4 was the new value. I think this should be as simple as
adding a value, but I kept on having difficulty.
Here you might want to either use the append() method on the lists of
each entry.
Any suggestions would be greatly appreciated.
I'm not sure what you are doing maps cleanly to currently existing
datastructures, which means that there might not be a quick shortcut for
you. Hammer out the specs of what you want your class to be able to do,
and what the API will be for performing each of those functions. Then
you should be able to begin implementing it, or at least come up with
some more specific questions.
Thank you very much,
Krishna
Cheers,
Cliff
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Re: A Bug By Any Other Name ...
On Sun, 2009-08-02 at 14:14 +, Albert van der Horst wrote: This is actually quite thoroughly untrue. In python, *indentation* is significant. Whitespace (internal to a line) is not. You can even call methods like this if you want: You totally don't get it. You describe how python is now. I propose a change to be made to python. Small wonder that that is different from what it is now. s = 'abc' s. upper() ABC You prove nothing by giving examples. You can disprove by giving one counter example, here it goes. Whitespace (internal to a line) is significant. In Python you cannot change xleftgoing = 12300 to x left going = 123 000 000 (You can in Algol68) I had a feeling that counterexample would be coming sooner or later. However, it doesn't really address the change you're looking for. Internal whitespace *is* irrelevant, except insofar as it can be used to delimit different tokens in parsing. If tokens are separate, they are separate, and no more or less whitespace is going to make any difference. Again, I'm describing how python is now. Which is not to say it couldn't be changed, I just want to make sure you understand how deep into the heart of python you are trying to cut. You make it sound like a small change, but it is not. You are proposing changing the parsing rules, which completely changes the scope of what is possible and what isn't with python syntax. All to solve a problem that, so far, hasn't been proven to exist in anything other than a speculative way. You're trying to turn an ocean liner around because you left your sunscreen on the dock. Cheers, Cliff -- http://mail.python.org/mailman/listinfo/python-list
Re: Help understanding the decisions *behind* python?
On Mon, 2009-07-20 at 12:26 -0700, Phillip B Oldham wrote:
On Jul 20, 6:08 pm, Duncan Booth duncan.bo...@invalid.invalid wrote:
The main reason why you need both lists and tuples is that because a tuple
of immutable objects is itself immutable you can use it as a dictionary
key.
Really? That sounds interesting, although I can't think of any real-
world cases where you'd use something like that.
Well, if you wanted to index a dictionary by coordinates, you might do
something like this:
fleet = {}
fleet[9,4] = 'destroyer'
fleet[8,4] = 'destroyer'
fleet[3,5] = 'aircraftcarrier'
fleet[4,5] = 'aircraftcarrier'
fleet[5,5] = 'aircraftcarrier'
fleet[6,5] = 'aircraftcarrier'
fleet[8,0] = 'battleship'
fleet[8,1] = 'battleship'
fleet[8,2] = 'battleship'
def checkattack(x, y, fleet):
if x,y in fleet:
return You hit my %s' % fleet[x,y]
Maybe not the best implementation of Battleship, but you get the idea.
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Re: A Bug By Any Other Name ...
On Fri, 2009-07-17 at 20:53 +, Albert van der Horst wrote: Because unlike in algol 68 in python whitespace is relevant, we could get by with requiring whitespace: x= -q # okay ab and -ac and -b -d# okay 8 ** -2 # okay This is actually quite thoroughly untrue. In python, *indentation* is significant. Whitespace (internal to a line) is not. You can even call methods like this if you want: s = 'abc' s. upper() ABC Obviously, that's A Bad Idea(tm), but python's parser won't stop you. The ++ operator gotcha is so minor that I can't remember anyone actually asking about it on the list (who was actually facing it as a problem--this thread was started by idle speculation). Can we not change the language syntax to address non-issues? Practicality beats purity, a.k.a. don't you have something better to do? Cheers, Cliff -- http://mail.python.org/mailman/listinfo/python-list
Re: mail
On Thu, 2009-07-16 at 00:16 +0530, amr...@iisermohali.ac.in wrote:
Dear all,
Sorry that I am disturbing you all again and again but this is the way I
am trying to solve my problem:---
import re
exp = re.compile(CA)
infile = open(file1.txt)
for line in infile:
... values = re.split(\s+, line)
... if exp.search(line):
...print (%s %s CA = %s %(values[2], values[3], values[6]))
...
with this it is giving the output like:
8 ALA CA = 54.67
15 ALA CA = 52.18
21 ALA CA = 54.33
23 ALA CA = 55.84
33 ALA CA = 55.58
38 ALA CA = 54.33
which is all right but i want CB and C value also in each row and it
should take value from 5th column infront of them, file is something
lookin like:-
47 8 ALA H H 7.85 0.02 1
48 8 ALA HAH 2.98 0.02 1
49 8 ALA HBH 1.05 0.02 1
50 8 ALA C C179.39 0.3 1
51 8 ALA CAC 54.67 0.3 1
52 8 ALA CBC 18.85 0.3 1
53 8 ALA N N123.95 0.3 1
10715 ALA H H 8.05 0.02 1
10815 ALA HAH 4.52 0.02 1
10915 ALA HBH 1.29 0.02 1
11015 ALA C C177.18 0.3 1
11115 ALA CAC 52.18 0.3 1
11215 ALA CBC 20.64 0.3 1
11315 ALA N N119.31 0.3 1
15421 ALA H H 7.66 0.02 1
15521 ALA HAH 4.05 0.02 1
15621 ALA HBH 1.39 0.02 1
15721 ALA C C179.35 0.3 1
15821 ALA CAC 54.33 0.3 1
15921 ALA CBC 17.87 0.3 1
16021 ALA N N123.58 0.3 1
16923 ALA H H 8.78 0.02 1
17023 ALA HAH 4.14 0.02 1
17123 ALA HBH 1.62 0.02 1
17223 ALA C C179.93 0.3 1
17323 ALA CAC 55.84 0.3 1
17423 ALA CBC 17.55 0.3 1
17523 ALA N N120.16 0.3 1
23233 ALA H H 7.57 0.02 1
23333 ALA HAH 3.89 0.02 1
23433 ALA HBH 1.78 0.02 1
23533 ALA C C179.24 0.3 1
23633 ALA CAC 55.58 0.3 1
23733 ALA CBC 19.75 0.3 1
23833 ALA N N121.52 0.3 1
26938 ALA H H 8.29 0.02 1
27038 ALA HAH 4.04 0.02 1
27138 ALA HBH 1.35 0.02 1
27238 ALA C C178.95 0.3 1
27338 ALA CAC 54.33 0.3 1
27438 ALA CBC 18.30 0.3 1
27538 ALA N N120.62 0.3 1
I just want that it will give output something like:-
8 ALA C = 179.39 CA = 54.67 CB = 18.85
15 ALA C = 177.18 CA = 52.18 CB = 20.64
21 ALA C = 179.35 CA = 54.33 CB = 17.87.
so first it will write the position of the amino acid(given by second
column)then amino acid here it is ALA and then the corresponding value of
C, CA and CB from 5th colum for each position of ALA.
Your program is structured wrong for doing what you want. Right now you
are essentially saying, for each line in the input file, print
something, but each line of the input file only has part of the
information you want. Instead, you should create a data structure that
gathers the pieces you want, and only print once you have all of those
pieces in place.
Step one, create your data structure, so the data is grouped the way you
want it, not by line:
thingies = {} # create a dictionary
for line in infile:
data = line.split()
if data[1] not in thingies:
# group data by data[1]
thingies[data[1]] = {}
thingies[data[1]][data[3]] = data[5]
Step two, extract the data from the list:
for key, data in thingies.items():
print key,
for entry in data
print '%s = %s' % (entry, data[entry]),
This should do what you want, minus some formatting issues.
Cheers,
Cliff
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Re: Clarity vs. code reuse/generality
On Fri, 2009-07-10 at 02:57 +, Steven D'Aprano wrote: On Fri, 10 Jul 2009 03:28:04 +0100, Nobody wrote: On Thu, 09 Jul 2009 04:57:15 -0300, Gabriel Genellina wrote: Nobody says you shouldn't check your data. Only that assert is not the right way to do that. assert is not the right way to check your *inputs*. It's a perfectly reasonable way to check data which should be valid, as well as a way to document what variables are supposed to contain. Where are those variables coming from? The distinction really boils down to this: * asserts should never fail. If there is any chance that an assertion might fail outside of test suites, then don't use assert. I'm no expert, but the more I read this thread, and the more I think on it, the more I believe that asserts don't really need to exist outside of test suites. The function that assertions provide is handled in a far more robust and maintainable way by unit tests and doctests. Anything else should be handled by more descriptive exceptions. The use of assertions in regular code may just be a historical baby step on the way to real code testing. To play devils advocate for a moment, one possible use case for assert statements is if you need to test something that you can't easily get under a proper unittest or doctest. Maybe you need to know the value of a variable halfway through a method. A judicious assertion can help supplement your test suite A better solution would be to refactor so you can get the needed value under test, but if time constraints won't allow it, then make your assertion and move on, but only to help you debug the code, not to protect your code at runtime. Even then, why not use a proper Exception (unless speed is a major issue)? Even if it is only used internally in a module, I would still prefer a ValueError to an AssertionError. It tells you what's happening more clearly. And it protects you if another caller (even one internal to the class) calls it with a different set of assumptions. At minimum, I think there's a heavy burden on an author to justify the use of AssertionErrors rather than other kinds of Exceptions. Cheers, Cliff -- http://mail.python.org/mailman/listinfo/python-list
Re: Clarity vs. code reuse/generality
On Fri, 2009-07-10 at 11:57 -0500, Robert Kern wrote: On 2009-07-10 11:50, J. Cliff Dyer wrote: On Fri, 2009-07-10 at 02:57 +, Steven D'Aprano wrote: On Fri, 10 Jul 2009 03:28:04 +0100, Nobody wrote: On Thu, 09 Jul 2009 04:57:15 -0300, Gabriel Genellina wrote: Nobody says you shouldn't check your data. Only that assert is not the right way to do that. assert is not the right way to check your *inputs*. It's a perfectly reasonable way to check data which should be valid, as well as a way to document what variables are supposed to contain. Where are those variables coming from? The distinction really boils down to this: * asserts should never fail. If there is any chance that an assertion might fail outside of test suites, then don't use assert. I'm no expert, but the more I read this thread, and the more I think on it, the more I believe that asserts don't really need to exist outside of test suites. Actually, there is a good argument that one shouldn't use an assert statement in test suites: code can have bugs that only show up under -O so you want to be able to run your test suite under -O. That's an interesting point. Presumably TestCase.assert_() doesn't suffer from this defect? Otherwise the entire unittest suite is essentially broken by your argument. I suppose I should have said one should only raise AssertionErrors in test suites. Practically speaking, that's what a test suite is: The place where you assert what the code does. -- http://mail.python.org/mailman/listinfo/python-list
Re: gett error message: TypeError: 'int' object is not callable
On Thu, 2009-07-09 at 13:53 +, Friðrik Már Jónsson wrote: Look at: len = len(text) You're overriding `len` (a built-in method), with an integer (`len(text)`). You then call: for i in range(len(fields)): But `len` is no longer a callable, but merely an integer. Regards, Friðrik Már P.S. While this is a fairly obvious problem it's usually a good idea to post working code and a traceback when requesting help. While we're on the subject of good question posting form: The body of your post should contain all relevant information. Please don't make readers look back at the subject heading for the statement of the problem. Duplicating the statement of the problem in the subject and the body is ok, but it really ought to be in the body. -- http://mail.python.org/mailman/listinfo/python-list
Re: Nested Classes and Instances
On Fri, 2009-07-10 at 19:00 +0200, Manuel Graune wrote: Hello, as an example of what I would like to achieve, think of a street where each house has a door and a sign with a unique (per house) number on it. I tried to model this like this: class House(object): class Door(object): def __init__(self,color): self.color=color class Sign(object): def __init__(self,text): self.text=text def __init__(self, doorcolor,housenumber): self.housenumber=housenumber self.door=House.Door(doorcolor) self.sign=House.Sign(housenumber) house1=House(red,1) house2=House(blue,2) Don't do it like that. Keep your classes independent. Many houses can have doors, and there's no reason to redefine the concept of Doors for each one. Same goes for Signs. class House(object): def __init__(self, doorcolor, housenumber): self.door = Door(doorcolor) self.sign = Sign(housenumber) self.number = housenumber class Door(object): def __init__(self, color): self.color = color class Sign(object): def __init__(self, inscription): self.inscription = str(housenumber) (Something like that) Cheers, Cliff Well, so far, so good. Now, what I'd like to achive is that the text of the sign changes whenever the variable housenumber of the parent-instance changes or that house1.sign.text is a reference/pointer to house1.housenumber Thanks in advance, Manuel -- A hundred men did the rational thing. The sum of those rational choices was called panic. Neal Stephenson -- System of the world http://www.graune.org/GnuPG_pubkey.asc Key fingerprint = 1E44 9CBD DEE4 9E07 5E0A 5828 5476 7E92 2DB4 3C99 -- http://mail.python.org/mailman/listinfo/python-list
Re: count
Bearophile wins! (This only times the loop itself. It doesn't check for __len__) summer:5 0:00:00.51 bearophile:5 0:00:00.09 summer:50 0:00:00.30 bearophile:50 0:00:00.13 summer:500 0:00:00.77 bearophile:500 0:00:00.53 summer:5000 0:00:00.000575 bearophile:5000 0:00:00.000473 summer:5 0:00:00.005583 bearophile:5 0:00:00.004625 summer:50 0:00:00.055834 bearophile:50 0:00:00.046137 summer:500 0:00:00.426734 bearophile:500 0:00:00.349573 summer:5000 0:00:04.180920 bearophile:5000 0:00:03.652311 summer:5 0:00:42.647885 bearophile: 5 0:00:35.190550 On Thu, 2009-07-09 at 04:04 -0700, Bearophile wrote: Paul Rubin: print x, sum(1 for _ in g) Don't use that, use my function :-) If g has a __len__ you are wasting time. And sum(1 ...) is (on my PC) slower. J. Clifford Dyer: if __name__ == '__main__': test_func(summer, 1000) test_func(tupler, 1000) test_func(summer, 1) test_func(tupler, 1) Have you forgotten my function? Bye, bearophile -- http://mail.python.org/mailman/listinfo/python-list
Re: tough-to-explain Python
On Thu, 2009-07-09 at 18:10 +, Steven D'Aprano wrote: If programming is symbol manipulation, then you should remember that the user interface is also symbol manipulation, and it is a MUCH harder problem than databases, sorting, searching, and all the other problems you learn about in academia. The user interface has to communicate over a rich but noisy channel using multiple under-specified protocols to a couple of pounds of meat which processes information using buggy heuristics evolved over millions of years to find the ripe fruit, avoid being eaten, and have sex. If you think getting XML was hard, that's *nothing* compared to user interfaces. +1 QOTW! QOTM, even! -- http://mail.python.org/mailman/listinfo/python-list
Re: Idioms and Anti-Idioms Question
On Wed, 2009-07-01 at 17:19 +1200, Lawrence D'Oliveiro wrote: In message mailman.2018.1245772229.8015.python-l...@python.org, J. Cliff Dyer wrote: If the lines got separated, a leading + could disappear into its line without any errors showing up. A trailing + would raise a syntax error. Unless, of course, it was moved onto the previous line as part of whatever caused the separation of the lines. How would you guard against that? Can you give an example of what you mean? -- http://mail.python.org/mailman/listinfo/python-list
Re: It's ...
On Tue, 2009-06-30 at 13:24 -0700, Beni Cherniavsky wrote:
On Jun 24, 11:40 pm, J. Cliff Dyer j...@sdf.lonestar.org wrote:
Also note that you can iterate over a file several times:
f = open('foo.txt')
for line in f:
print line[0] # prints the first character of every line
for line in f:
print line[1] #prints the second character of every line
No, you can't. The second loop prints nothing!
A file by default advances forward. Once you reach the end, you stay
there.
You are, of course, absolutely right. Sorry for the misinformation.
:(
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Re: Get name of class without instance
On Wed, 2009-06-24 at 09:17 -0700, Bryan wrote: Given a class: class Foo(object): pass How can I get the name Foo without having an instance of the class? str(Foo) gives me more than just the name Foo. __main__.Account Foo.__class__.__name__ gives me type I don't want to do: Foo().__class__.__name__ if possible. I would rather avoid the constructor. I just want to get a string Foo I'll give you a hint: Foo().__class__ is Foo True -- http://mail.python.org/mailman/listinfo/python-list
Re: It's ...
On Wed, 2009-06-24 at 20:53 +0100, Angus Rodgers wrote:
... my first Python program! So please be gentle (no fifty ton
weights on the head!), but tell me if it's properly Pythonic,
or if it's a dead parrot (and if the latter, how to revive it).
Yay. Welcome to Python.
I'm working from Beazley's /Python: Essential Reference/ (2nd
ed. 2001), so my first newbie question is how best to find out
what's changed from version 2.1 to version 2.5. (I've recently
installed 2.5.4 on my creaky old Win98SE system.) I expect to
be buying the 4th edition when it comes out, which will be soon,
but before then, is there a quick online way to find this out?
Check here: http://docs.python.org/whatsnew/index.html
It's not designed to be newbie friendly, but it's in there.
Having only got up to page 84 - where we can actually start to
read stuff from the hard disk - I'm emboldened to try to learn
to do something useful, such as removing all those annoying hard
tab characters from my many old text files (before I cottoned on
to using soft tabs in my text editor).
This sort of thing seems to work, in the interpreter (for an
ASCII text file, named 'h071.txt', in the current directory):
stop = 3 # Tab stops every 3 characters
from types import StringType # Is this awkwardness necessary?
Not anymore. You can just use str for this.
detab = lambda s : StringType.expandtabs(s, stop) # Or use def
First, use def. lambda is a rarity for use when you'd rather not assign
your function to a variable.
Second, expandtabs is a method on string objects. s is a string object,
so you can just use s.expandtabs(stop)
Third, I'd recommend passing your tabstops into detab with a default
argument, rather than defining it irrevocably in a global variable
(which is brittle and ugly)
def detab(s, stop=3):
#do stuff
Then you can do
three_space_version = detab(s)
eight_space_version = detab(s, 8)
f = open('h071.txt') # Do some stuff to f, perhaps, and then:
f.seek(0)
f is not opened for writing, so if you do stuff to the contents of f,
you'll have to put the new version in a different variable, so f.seek(0)
doesn't help. If you don't do stuff to it, then you're at the beginning
of the file anyway, so either way, you shouldn't need to f.seek(0).
print ''.join(map(detab, f.xreadlines()))
Sometime in the history of python, files became iterable, which means
you can do the following:
for line in f:
print detab(line)
Much prettier than running through join/map shenanigans. This is also
the place to modify the output before passing it to detab:
for line in f:
# do stuff to line
print detab(line)
Also note that you can iterate over a file several times:
f = open('foo.txt')
for line in f:
print line[0] # prints the first character of every line
for line in f:
print line[1] #prints the second character of every line
f.close()
Obviously, to turn this into a generally useful program, I need
to learn to write to a new file, and how to parcel up the Python
code, and write a script to apply the detab function to all the
files found by searching a Windows directory, and replace the old
files with the new ones; but, for the guts of the program, is this
a reasonable way to write the code to strip tabs from a text file?
For writing the output file, this seems to work in the interpreter:
g = open('temp.txt', 'w')
g.writelines(map(detab, f.xreadlines()))
g.close()
Doesn't help, as map returns a list. You can use itertools.imap, or you
can use a for loop, as above.
In practice, does this avoid creating the whole string in memory
at one time, as is done by using ''.join()? (I'll have to read up
on opaque sequence objects, which have only been mentioned once
or twice in passing - another instance perhaps being an xrange()?)
Not that that matters much in practice (in this simple case), but
it seems elegant to avoid creating the whole output file at once.
The terms to look for, rather than opaque sequence objects are
iterators and generators.
OK, I'm just getting my feet wet, and I'll try not to ask too many
silly questions!
First impressions are: (1) Python seems both elegant and practical;
and (2) Beazley seems a pleasantly unfussy introduction for someone
with at least a little programming experience in other languages.
Glad you're enjoying Beazley. I would look for something more
up-to-date. Python's come a long way since 2.1. I'd hate for you to
miss out on all the iterators, booleans, codecs, subprocess, yield,
unified int/longs, decorators, decimals, sets, context managers and
new-style classes that have come since then.
--
Angus Rodgers
Cheers,
Cliff
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Re: Procedures
Please keep the discussion on-list. (Reply-all, rather than just
replying to me.)
On Mon, 2009-06-22 at 15:36 -0700, Greg Reyna wrote:
It's not the error that concerned me. The fact that there is an
error of this type makes clear that there's something wrong with the
way the scripts are structured. I was trying to communicate that I
recognized this fact. Clearly, I was not successful. Thought I'd
try to save bandwidth, too.
...
I had tried running this previously with only one Class header:
LineReader, the others were just defs. I changed the short defs
into sub-classes out of desperation, since I don't understand why the
main script is not recognizing functions that are in the same file.
First is the shell input/output, then ParseWork.py, the entire text
file that contains the scripts.
Thanks for your interest, Cliff,
Greg
---
import ParseWork
avar = ParseWork.LineReader()
xstring = 'scene 1, pnl 1, 3+8, pnl 2, 1+12, pnl 3, 12, pnl 4, 2+4,'
avar.parseLine(xstring)
Traceback (most recent call last):
File stdin, line 1, in module
File ParseWork.py, line 13, in parseLine
xreturn = advanceSearch(xstring) #shorten the part of string to
be searched
NameError: global name 'advanceSearch' is not defined
---
class LineReader:
def parseLine(self, xstring):
global sc_info,scnum,pnlnum,prev_pos,cur_pos
sc_info = { 'sc':{0:0}} #dict to store scene num; pnl num(s), ftge
prev_pos = 0
cur_pos = xstring.find(',') #defaults to length of string
while xstring.find(',',(prev_pos+1)) != -1:
temp = xstring[prev_pos:cur_pos] #pull out the part btwn commas
section = temp.strip()
if section[0:1] == 's':
scnum = int(section[5:]) #get the number(s) off the
end of scene block
sc_info['sc',scnum] = scnum #store scnum-which is
both key and value
xreturn = advanceSearch(xstring) #shorten the part
of string to be searched
continue
if section[0:1] == 'p':
pnlnum = int(section[3:])
sc_info['sc',scnum,pnlnum] = pnlnum #store pnlnum
temp value for pnlnum
xreturn = advanceSearch(xstring) #the return value
is to move flow back here
continue
if section[0:1] != 's' or 'p':
xnum = section[0:] #section must contain the footage
if section.find('+'): #the + exists
ftge = parseFtge(section)
sc_info['sc',scnum,pnlnum] = ftge #store ftge in pnlnum
xreturn = advanceSearch(xstring)
continue
else:
ftge = (section/16.0) #section is frames-convert
to decimal
sc_info['sc',scnum,pnlnum] = ftge #store ftge in pnlnum
xreturn = advanceSearch(xstring)
continue
else:
print sc_info
class ContRead(LineReader):
def advanceSearch(xstring):
prev_pos = (cur_pos +1)
cur_pos = xstring.find(',',prev_pos) #find the next comma
return
class Footage(LineReader):
def parseFtge(section):
xplus = section.find('+') #find position of '+'
xfeet = int(section[0:xplus])
xframes = int(section[(xplus + 1):-1])
xframes_d = (xframes/16.0)
return (xfeet + xframes_d)
From what I can see you have no need for classes in your code. This is
probably what is causing you trouble at the moment, so I would say just
remove them.
def parse_line(line):
splits a line on commas
return line.split(',')
def parse_footer(line):
Strips off leading four characters (maybe 'Ftr:'), and then
parses the rest as above
return parse_line([4:])
That should solve your problem. Below I illustrate some of how classes
work, in case you are dead set on using them. Learning Python should
address all of this as well. I haven't read it, so I can't be more
specific.
To call a method from another method within a class, you need to prefix
it with self. That looks like this:
class Spam(object): ## {1}
def parse_line(self, line): ## {2}
return line.split(',')
def parse_footer(self, line):
return self.parse_line(line[4:]) ## {3}
# {1} always subclass 'object' to use newstyle classes
# {2} Note that method declarations have an extra first argument,
# usually called self, which refers to your instance of the class.
# {3} self finds parse_line within the current class
# or superclasses of the current class. Note that self has
# moved from inside the parentheses to before the method name.
To call a method from another class you need to instantiate that class
first.
class Spam(object):
Re: Idioms and Anti-Idioms Question
On Mon, 2009-06-22 at 22:52 +, Peter Billam wrote: I wonder on what grounds PEP8 says The preferred place to break around a binary operator is *after* the operator ? Perhaps it's just the continutation marker rationale? Regards, Peter -- Peter Billam www.pjb.com.auwww.pjb.com.au/comp/contact.html If the lines got separated, a leading + could disappear into its line without any errors showing up. A trailing + would raise a syntax error. spam = 6 spam + File stdin, line 1 spam + ^ SyntaxError: invalid syntax + spam 6 -- http://mail.python.org/mailman/listinfo/python-list
Re: Perl's @foo[3,7,1,-1] ?
On Mon, 2009-06-22 at 14:57 +0200, Jean-Michel Pichavant wrote: J. Cliff Dyer wrote: On Wed, 2009-06-17 at 14:13 +0200, Jean-Michel Pichavant wrote: On Wed, Jun 17, 2009 at 04:14, Steven D'Aprano wrote: What's np.arange? import numpy as np -- Pierre delroth Bourdon delr...@gmail.com Étudiant à l'EPITA / Student at EPITA Perfect example of why renaming namespaces should be done only when absolutely required, that is, almost never. Jean-Michel I disagree. Renaming namespaces should always be done if it will help stop people from doing a 'from package import *'. However, example code should always include relevant imports. Cheers, Cliff The import * should not used if possible, I totally agree on that point, but there's no need to rename namespaces for that. br Jean-Michel Technically, no. But we're dealing with people, who are notoriously *un*technical in their behavior. A person is much more likely to develop bad habits if the alternative means more work for them. The reason people do `from foo import *` is that they don't want to type more than they have to. If they can write a one or two letter namespace, they're likely to be happy with that trade-off. If the alternative is to write out long module names every time you use a variable, they'll tend to develop bad habits. To paraphrase Peter Maurin, coding guidelines should have the aim of helping to bring about a world in which it is easy to be good. I don't really see much problem with renaming namespaces: For people reading the code, everything is explicit, as you can just look at the top of the module to find out what module a namespace variable represent; the local namespace doesn't get polluted with God knows what from God knows where; and code remains succinct. I've found in my own code that using, for example, the name `sqlalchemy` in my code means that I have to go through painful contortions to get your code down to the PEP-8 recommended 80 characters per line. The resulting mess of multi-line statements is significantly less readable than the same code using the abbreviation `sa`. Do you have an argument for avoiding renaming namespaces? So far the only example you provided is a code fragment that doesn't run. I don't disagree with you on that example; referring to numpy as np without telling anyone what np refers to is a bad idea, but no functioning piece of code could reasonably do that. Cheers, Cliff -- http://mail.python.org/mailman/listinfo/python-list
Re: How to output a complex List object to a file.
Have you looked at the JSON module?
On Mon, 2009-06-22 at 21:17 +0800, Jim Qiu wrote:
Hi all,
I have a object list list this:
from bots.botsconfig import *
from D96Arecords import recorddefs
from edifactsyntax3 import syntax
structure=[
{ID:'UNH',MIN:1,MAX:1,LEVEL:[
{ID:'BGM',MIN:1,MAX:1},
{ID:'DTM',MIN:1,MAX:5},
{ID:'NAD',MIN:1,MAX:5,LEVEL:[
{ID:'CTA',MIN:0,MAX:5,LEVEL:[
{ID:'COM',MIN:0,MAX:5},
]},
]},
{ID:'RFF',MIN:0,MAX:5,LEVEL:[
{ID:'DTM',MIN:0,MAX:5},
]},
{ID:'CUX',MIN:0,MAX:5,LEVEL:[
{ID:'DTM',MIN:0,MAX:5},
]},
{ID:'LOC',MIN:1,MAX:20,LEVEL:[
{ID:'DTM',MIN:0,MAX:5},
{ID:'LIN',MIN:0,MAX:20,LEVEL:[
{ID:'PIA',MIN:0,MAX:5},
{ID:'IMD',MIN:0,MAX:5},
{ID:'RFF',MIN:0,MAX:5},
{ID:'ALI',MIN:0,MAX:5},
{ID:'MOA',MIN:0,MAX:5},
{ID:'PRI',MIN:0,MAX:5},
{ID:'QTY',MIN:0,MAX:999,LEVEL:[
{ID:'NAD',MIN:0,MAX:1},
]},
]},
]},
{ID:'UNT',MIN:1,MAX:1},
]
}
]
I need to output this structure object into a file, how to do that ?
Jim
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Re: Procedures
On Mon, 2009-06-22 at 12:13 -0700, Greg Reyna wrote: Learning Python (on a Mac), with the massive help of Mark Lutz's excellent book, Learning Python. What I want to do is this: I've got a Class Object that begins with a def. It's designed to be fed a string that looks like this: scene 1, pnl 1, 3+8, pnl 2, 1+12, pnl 3, 12, pnl 4, 2+4, I'm parsing the string by finding the commas, and pulling out the data between them. No problem so far (I think...) The trouble is, there is a place where code is repeated: 1. Resetting the start end position and finding the next comma in the string. Have you looked at the split() method on string objects. It works kind of like this: s = scene 1, pnl 1, 3+8, pnl 2, 1+12, pnl 3, 12, pnl 4, 2+4, s.split(,) ['scene 1', ' pnl 1', ' 3+8', ' pnl 2', ' 1+12', ' pnl 3', ' 12', ' pnl 4', ' 2+4', ''] elements = s.split(,) elements ['scene 1', ' pnl 1', ' 3+8', ' pnl 2', ' 1+12', ' pnl 3', ' 12', ' pnl 4', ' 2+4', ''] elements[2] ' 3+8' In my previous experience (with a non-OOP language), I could create a 'procedure', which was a separate function. With a call like: var=CallProcedure(arg1,arg2) the flow control would go to the procedure, run, then Return back to the main function. Python doesn't have procedures quite like this. It has functions (the things starting with def), which generally speaking take arguments and return values. For the most part, you do not want your functions to operate on variables that aren't either defined in the function or passed in as arguments. That leads to difficult-to-debug code. In Python, when I create a second def in the same file as the first it receives a undefined error. I can't figure out how to deal with this. How do I set it up to have my function #1 call my function #2, and return? Your problem description is confusing. First of all, no class starts with 'def'. They all start with 'class'. Perhaps you are talking about a module (a python file)? Also, telling us that you get an undefined error is not particularly helpful. Every Exception that python raises is accompanied by an extensive stack trace which will help you (or us) debug the problem. If you don't show us this information, we can't tell you what's going wrong. It will tell you (in ways that are crystal clear once you have a bit of practice reading them) exactly what went wrong. Can you show your code, as well as the complete error message you are receiving? My suggestions here, are essentially a paraphrasing of Eric Raymond's essay, How to Ask Smart Questions. It is freely available on the web, and easily found via google. I recommend reading that, in order to get the most mileage out this news group. Cheers, Cliff -- http://mail.python.org/mailman/listinfo/python-list
Re: Perl's @foo[3,7,1,-1] ?
On Wed, 2009-06-17 at 14:13 +0200, Jean-Michel Pichavant wrote: On Wed, Jun 17, 2009 at 04:14, Steven D'Aprano wrote: What's np.arange? import numpy as np -- Pierre delroth Bourdon delr...@gmail.com Étudiant à l'EPITA / Student at EPITA Perfect example of why renaming namespaces should be done only when absolutely required, that is, almost never. Jean-Michel I disagree. Renaming namespaces should always be done if it will help stop people from doing a 'from package import *'. However, example code should always include relevant imports. Cheers, Cliff -- http://mail.python.org/mailman/listinfo/python-list
Re: Perl's @foo[3,7,1,-1] ?
On Sun, 2009-06-14 at 23:01 +1000, Steven D'Aprano wrote: Write a helper function: def getitems(L, *indexes): if len(indexes) == 1: indexes = indexes[0] return [L[i] for i in indexes] Whoops! Your example is broken: cars = ['Ford', 'Toyota', 'Edsel'] getitems(cars, 1) Traceback (most recent call last): File stdin, line 1, in module File stdin, line 4, in getitems TypeError: 'int' object is not iterable I think you meant to apply that [0] to the created list instead. Something like: def getitems(L, *indexes): new_list = [L[i] for i in indexes] if len(indexes) == 1: new_list = new_list[0] return new_list But I'm not sure that would be the best idea anyway. Just let getitems always return a list. That way the caller doesn't have to test the length to figure out what to do with it. If you know you want a single item, you can use regular old .__getitem__ (or .get) methods, or direct indexing. Then getitems can just be: def getitems(L, *indexes): return [L[i] for i in indexes] But I think this is an obvious enough extension to the __getitem__ protocol that I for one would vote +1 on it being added to Python sequence objects (lists, tuples, strings). I'd be +0. It won't change my life, but it seems like a decent idea. -- Steven Cheers, Cliff -- http://mail.python.org/mailman/listinfo/python-list
Re: reseting an iterator
On Wed, 2009-05-20 at 11:35 -0700, Jan wrote: Wouldn't it be easy for Python to implement generating functions so that the iterators they return are equipped with a __reset__() method? Here is the context of this question. Python documentation defines a iterator as an object ITERATOR having methods __next__() and __iter__() such that the call ITERATOR.__iter__() returns the object itself, and once a call ITERATOR. __next__() raises StopIteration every such subsequent call does the same. You don't need a reset method. There is no hard and fast rule that __iter__ must return the object itself. It just needs to return an iterator. For example: l = [1,2,3] l.__iter__() listiterator object at 0x7fd0da315850 l is l.__iter__() False Just create a class with an __iter__ method that returns a reset iterator object. class X(object): def __init__(self, max=3): self.counter = 0 self.max = max def __iter__(self): return self def next(self): if self.counter self.max: self.counter += 1 return self.counter else: raise StopIteration class Y(object): def __iter__(self): return X() In this setup, X has the problem you are trying to avoid, but Y behaves as a resettable iterable. x = X() for c in x: ... print c ... 1 2 3 for c in x: ... print c ... y = Y() for c in y: ... print c ... 1 2 3 for c in y: ... if c 3: ... print c ... 1 2 for c in y: ... print c ... 1 2 3 Cheers, Cliff -- http://mail.python.org/mailman/listinfo/python-list
Re: While Statement
On Fri, 2009-05-22 at 09:59 -0400, Dave Angel wrote: Tim Wintle wrote: On Fri, 2009-05-22 at 13:19 +0200, Andre Engels wrote: number/total = 998/999 = 0 number/total*100 = 0*100 = 0 float(number/total*100) = float(0) = 0.0 Change float(number/total*100) to float(number)/total*100 and it should work: I'd use: (number * 100.)/total - works because int * float = float It's a minor thing, but it's much faster to cast implicitly as you miss the python function call overhead - it's no extra work to write, and for numerical things it can really speed things up. a = timeit.Timer(float(200)/5*100) b = timeit.Timer((200*100.)/5) a.timeit(1000) 12.282480955123901 b.timeit(1000) 3.6434230804443359 Tim W It's the old-timer in me, but I'd avoid the float entirely. You start with ints, and you want to end with ints. So simply do the multiply first, then the divide. number * 100/total will get the same answer. Also, to get the same behavior (faster integer division) in python 3 or when using `from __future__ import division`, use the // division operator instead of /. In fact, a little experimentation shows that you get the speedup even when using python 2.6 with old-style division. Probably because python doesn't have to check the types of its arguments before deciding to do integer division. a = timeit.Timer((200 * 100.)/5) b = timeit.Timer((200 * 100)/5) c = timeit.Timer((200 * 100)//5) d = timeit.Timer((200 * 100.0)//5) for each in a, b, c, d: ... each.timeit() ... 2.3681092262268066 2.417525053024292 0.81031703948974609 0.81548619270324707 Cheers, Cliff -- http://mail.python.org/mailman/listinfo/python-list
Re: Question about locals()
Top-posting corrected.
On Fri, 2009-05-22 at 10:00 -0500, Gökhan SEVER wrote:
On Fri, May 22, 2009 at 9:43 AM, David Robinow drobi...@gmail.com
wrote:
On Fri, May 22, 2009 at 10:27 AM, Gökhan SEVER
gokhanse...@gmail.com wrote:
...
serialc = np.loadtxt(sys.argv[1], skiprows=skiprows).T
for i in range(20):
locals()['serialc_bin' + str(i+1)] = serialc[i+4]
I don't know easier way than using locals() to construct
variable-like
identities in my program.
I don't either. I also don't know why you feel you need to
construct
variable-like identities.
Why is:
serialc_bin1
better than
serialc_bin[0]
or, for that matter,
serialc[4]
???
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Because in this case serialc is an numpy array. Since loadtxt returns
a numpy-array. Furthermore
locals()['serialc_bin' + str(i+1)] creates a dictionary key (that's
what I use the term variable-like) serialc_bin1, serialc_bin2, ...
not serialc_bin[0] with indexes.
Gökhan
I'm not sure why dictionary keys are better than indexes in your
example, especially as they're being created by coercing integers to
strings. However, that's your business. But why not just create your
own dictionary. Then you can pass the results around easily as a group
or one at a time, and you don't have to mess in locals() (which isn't
supposed to be messed in). It also gives you more flexibility as to how
you name your entries:
d = {}
You can use the same indexes you're using now:
d['serialc_bin' + str(i+1)] = serialc[i+4]
or you can keep the integerness of i by using tuples as keys (thus
preserving sort order across your keys):
d[('serialc_bin', i+1)] = serialc[i+4]
or you can use the integer as a key by itself (yes! It looks like
you're accessing a list, but it's actually a dict with integer keys):
d[i+1] = serialc[i+4]
Or you can use a dict with a more descriptive name and the last above
solution gains the readability of your initial solution:
serialc_bin = {}
serialc_bin[i+1] = serialc[i+4]
Finally, if there's more you want to do with these numbers, you can
create a class to hold them. Then as you need to, you can add methods
to it to implement the behavior you're looking for.
class MyCollection(object):
Untested code
def __init__(self):
self._store = {}
def __getitem__(self, item):
return self._store[item]
def __setitem__(self, item, value):
self._store[item] = value
def __delitem__(self, item):
del(self._store[item])
def sum(self):
total = 0
for value in self._store.values():
total += value
return value
serialc_bin = MyCollection()
for i, value in enumerate(serialc):
serialc_bin[i+1] = value
print serialc_bin.sum()
Any one of these seems like a better idea to me than trying to pollute
your local namespace with an unknown number of variables. You have a
collection of objects. It makes sense to store them in one of python's
collection types, or create an object of your own to store them.
Cheers,
Cliff
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Re: reseting an iterator
On Fri, 2009-05-22 at 10:54 -0700, Jan wrote: On May 22, 9:46 am, J. Cliff Dyer j...@sdf.lonestar.org wrote: You don't need a reset method. There is no hard and fast rule that __iter__ must return the object itself. It just needs to return an iterator. I disagree. If ITRATOR is a true iterator, ITRATOR.__iter__() must return ITERATOR. If ITERABLE is an iterable (but not necessarily an iterator) ITRABLE.__iter__() must return an iterator. You are correct: It is an iterable, not an iterator. However, that's not a disagreement with me. It may not be an iterator (and I probably should have said so) but it works, and it solves the OP's problem. For example: l = [1,2,3] l.__iter__() listiterator object at 0x7fd0da315850 l is l.__iter__() False [1,2,3] is an iterable but not an iterator, so this False result is expected. Compare this with the following. ii = iter([1,2,3]) # ii is an iterator. next(ii) 1 jj = ii.__iter__() # call __iter__ method on an iterator ii is jj True next(jj) 2 Just create a class with an __iter__ method that returns a reset iterator object. class X(object): def __init__(self, max=3): self.counter = 0 self.max = max def __iter__(self): return self def next(self): if self.counter self.max: self.counter += 1 return self.counter else: raise StopIteration class Y(object): def __iter__(self): return X() In this setup, X has the problem you are trying to avoid, but Y behaves as a resettable iterable. y = Y() This does not work. With this, y is not an interator, and not even an iterable. for c in y: This produces an error because by definition of for-loops it is executed the same way as: temp_iterator = iter(y) # temp_iterator is y while True: try: print(next(temp_iterator)) # temp_iterator does not support __next__() except StopIteration: break Did you try running my code? I did. It works on my computer. What error message did you get? Cheers, Cliff -- http://mail.python.org/mailman/listinfo/python-list
Re: Sorting a dictionary
On Fri, 2009-05-15 at 09:57 -0700, Tobiah wrote: On Tue, 12 May 2009 14:17:54 +0200, Jaime Fernandez del Rio wrote: This one I think I know... Try with: for k in sorted(word_count) : print k,=,word_count[k] You need to do the sorting before iterating over the keys... Isn't that what's happening here? I read this as the 'sorted' function iterating over the keys in word_count, then passing that sorted list to the 'for' loop, for a second iteration over the sorted pairs. No? Tobiah The code and the description you are responding to are by the same poster. The OP posted something quite different. @Ronn: The for statement, which is the line ending with : has all the control over what order elements get processed in. Compare the following cases: for x in ['hat', 'socks', 'shirt', 'pants']: ... print sorted(x) aht ckoss hirst anpst In this case, each element of the list gets sorted. That is, the letters of each string are put in alphabetical order. But they are processed in the order they appeared in the list. If you want to process the elements of the list in alphabetical order, you have to sort the list itself: for x in sorted(['hat', 'socks', 'shirt', 'pants']): ... print x hat pants shirt socks Cheers, Cliff -- http://mail.python.org/mailman/listinfo/python-list
Re: How to see the code definiton in the shell ?
On Wed, 2009-05-13 at 09:40 -0700, Mohan Parthasarathy wrote: Hi, I am new to Python. I tried searching this but could not find an answer. In the interactive shell, I write a new function and I want to be able to see all the code that I wrote at a later time. Just typing the function name only shows allmethods function allmethods at 0x822b0 How do I see the actual code ? thanks mohan The function definition itself has been compiled down to bytecode. You can see the bytecode as follows: def one(): ... return 1 ... print one.func_code.co_code # not very readable 'd\x01\x00S' import dis # python disassembler dis.dis(one.func_code.co_code) 0 LOAD_CONST 1 (1) 3 RETURN_VALUE or just run dis.dis on the function itself def two(): ... import math ... return (math.e ** (0+1J*math.pi)) + 3 ... two() (2+1.2246063538223773e-16j) two.func_code.co_code 'd\x01\x00d\x00\x00k\x00\x00}\x00\x00|\x00\x00i\x01\x00d\x02\x00d\x03 \x00|\x00\x00i\x02\x00\x14\x17\x13d\x04\x00\x17S' dis.dis(two) 2 0 LOAD_CONST 1 (-1) 3 LOAD_CONST 0 (None) 6 IMPORT_NAME 0 (math) 9 STORE_FAST 0 (math) 3 12 LOAD_FAST0 (math) 15 LOAD_ATTR1 (e) 18 LOAD_CONST 2 (0) 21 LOAD_CONST 3 (1j) 24 LOAD_FAST0 (math) 27 LOAD_ATTR2 (pi) 30 BINARY_MULTIPLY 31 BINARY_ADD 32 BINARY_POWER 33 LOAD_CONST 4 (3) 36 BINARY_ADD 37 RETURN_VALUE -- http://mail.python.org/mailman/listinfo/python-list
Re: unicode bit me
On Fri, 2009-05-08 at 07:53 -0700, anuraguni...@yahoo.com wrote:
#how can I print a list of object which may return unicode
representation?
# -*- coding: utf-8 -*-
class A(object):
def __unicode__(self):
return u©au
__str__ = __repr__ = __unicode__
Your __str__ and __repr__ methods don't return strings. You should
encode your unicode to the encoding you want before you try to print it.
class A(object):
def __unicode__(self):
return u©au
def get_utf8_repr(self):
return self.__unicode__().encode('utf-8')
def get_koi8_repr(self):
return self.__unicode__().encode('koi-8')
__str__ = __repr__ = self.get_utf8_repr
a = A()
try:
print a # doesn't work?
except UnicodeEncodeError,e:
print e
try:
print unicode(a) # works, ok fine, great
except UnicodeEncodeError,e:
print e
try:
print unicode([a]) # what doesn't work?
except UnicodeEncodeError,e:
print e
Now how can I print a list of object which may return unicode
representation?
loop/map is not an option as it goes much deepr in my real code
any can anyoen explain what is happening here under the hood?
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Re: php to python code converter
On Fri, 2009-05-08 at 17:19 +0200, Pascal Chambon wrote: PS : Am I the only one having most of answers rejected by the antispam system of python-list ? That's humiliating :p I've had several messages not make it through. :( -- http://mail.python.org/mailman/listinfo/python-list
Re: for with decimal values?
On Sun, 2009-05-03 at 19:48 -0700, alex23 wrote: On May 4, 11:41 am, Esmail ebo...@hotmail.com wrote: All this discussion makes me wonder if it would be a good idea for Python to have this feature (batteries included and all) - it would have its uses, no? Well, sometimes more discussion == less consensus :) But it's really easy to roll your own: from decimal import Decimal def args2dec(fn): '''*args to Decimal decorator''' float2dec = lambda f: Decimal(str(f)) def _args2dec(*args): args = map(float2dec, args) return fn(*args) return _args2dec @args2dec def drange(start, stop, step): while start stop: yield start start += step I'd prefer not to force my users into using the Decimal type. Maybe float fits their needs better. So here's a generalized xrange replacement, which fixes an error in the drange implementation above (try it with a negative step). It's also highly *not* optimized. Calculating i * step every time slows it down. Speeding it back up is an exercise for the reader. def general_xrange(start, stop, step=1): target = stop * step if start * step target: raise ValueError i = start while i * step target: yield i i += step Cheers, Cliff -- http://mail.python.org/mailman/listinfo/python-list
Re: Re: list comprehension question
On Fri, 2009-05-01 at 13:00 -0400, John Posner wrote: Shane Geiger wrote: if type(el) == list or type(el) is tuple: A tiny improvement: if type(el) in (list, tuple): Another alternative, which might be useful in some cases: if hasattr(el, '__iter__'): This covers all iterables, not just lists and tuples. So: flatten([1,2, xrange(3,15), 15, 16]) [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16] The downside, of course, is that some iterables might be infinite (such as count), which would cause hidden breakage. But if you have one of those in your data structure, why are you trying to flatten it anyway? Cheers, Cliff -- http://mail.python.org/mailman/listinfo/python-list
Re: list comprehension question
On Tue, 2009-05-05 at 12:15 -0400, J Kenneth King wrote: Emile van Sebille em...@fenx.com writes: On 5/1/2009 7:31 AM J Kenneth King said... Chris Rebert c...@rebertia.com writes: b = [] for pair in a: for item in pair: b.append(item) This is much more clear than a nested comprehension. I love comprehensions, but abusing them can lead to really dense and difficult to read code. I disagree on dense and difficult, although I'll leave open the question of abuse. Dense and difficult may be subjective to people like you or I, but you left out the to read part of that sentence. I was referring to the negative effect nested or complex list comprehensions can have on readability. b = [ item for pair in a for item in pair ] It's a clever statement, but use it once and its gone. Why not use the expanded form in a function definition and get an even shorter, but clearer statement? It's also not obvious what it means. I would have thought the proper incantation would be: [item for item in pair for pair in a] but that returns [5,5,5,6,6,6]. I still haven't figured out why. The way you have to bounce your eyes back and forth in the comprehension makes it hard to read the logic. With the loop, on the other hand it is blatantly obvious which way the nesting occurs. b = flatten(a) Boom, done. This is exactly the code above expressed in comprehension form. It's worth knowing that a list comprehension is structured identically to the equivalent for loop. So it really is neither more dense nor more difficult to read. Further, you can tell immediately from the start of the list comprehension what you've got -- in this case a list of item(s). Empirically, I'd have to disagree with you. The structure is changed by the fact that item gets put at the beginning of the comprehension. With the loop, each variable gets introduced in a for statement, and then used. With the list comprehension, item gets used at the beginning, and then assigned to in the for expression at the end. Meanwhile, pair gets introduced as the loop variable in the first for expression, and iterated over in the second for expression. So do you read it left to right or right to left? Neither. You have to hold the whole expression in your mind at once. Good for short and simple comprehensions, bad as they get more complicated. Here with some slight changes... a = [(1, 2), (3, 4, 7), (5, 6)] [ item for j in a if len(j)==2 for item in j if item % 2 ] [1, 5] This, to me, looks like line noise, approaching perl in its unreadability. ...opposed to... for j in a: ... if len(j)==2: ... for item in j: ... if item % 2: ... b.append(item) ... b [1, 5] Much nicer. Thank you. Thanks for the lesson in list comprehensions, but I'm well aware of how they work. List comprehensions can make a reader of your code apprehensive because it can read like a run-on sentence and thus be difficult to parse. The Python documentation discourages their use and I believe for good reason. It's much easier to explain complex processes with a function rather than a single nested statement. YMMV, Emile It will apparently vary greatly. Depending on how much coffee I've had. ;) J -- http://mail.python.org/mailman/listinfo/python-list -- http://mail.python.org/mailman/listinfo/python-list
Re: dict is really slow for big truck
On Wed, 2009-04-29 at 10:05 -0700, Scott David Daniels wrote:
Bruno Desthuilliers wrote:
d = {}
for line in open(thefile):
arr = line.strip().split()
d[arr[0]] = arr
Sorry, not picking on Bruno in particular, but I keep seeing
this formulation around various places.
When does line.strip().split() ever differ from line.split()?
Good question. I can't count the number of times I've used
line.strip().split() in my own code, just because I didn't 1) read the
documentation closely enough, or 2) try the alternative, but lo and
behold, they are the same, at least in the cases I was trying to account
for.
' a b c '.split() == ' a b c '.strip().split() == 'a b c'.split()
Thanks for pointing this out.
Cheers,
Cliff
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Re: Restart generator when it is exhausted.
On Tue, 2009-04-28 at 10:41 +, Duncan Booth wrote:
Lacrima lacrima.ma...@gmail.com wrote:
If it is not possible what are common techniques to use iterator or
generator objects that allow restarting when it is needed?
The usual thing if you want to use the generator's output more than once
would be to convert the generator to a list, then you can iterate over it
as often as you want.
a = ['a', 'b', 'c']
g = (i for i in a)
restartable = list(g)
If you want the output of the generator to potentially change each time you
iterate then you need to create a new generator.
More verbosely, but without putting your generator in , you can use the
iterator protocol to create a reusable iterable:
An iterable is a class with an __iter__ method that returns an iterator.
So for example:
class Iterator(object):
def __init__(self, filename):
self.f = open(filename)
def __iter__(self):
return self
def next(self):
line = self.f.readline()
if not line:
raise StopIteration
return line.strip()[:8]
is an iterator (which is also an iterable), which will grab each line of
a file, returning the first eight non-whitespace characters until the
file is used up. Then the iterator is exhausted, and will continue to
raise StopIteration each time it is called.
class Iterable(object):
def __init__(self, filename):
self.filename = filename
def __iter__(self):
return Iterator(self.filename)
This is a reusable iterable which returns a new instance of the Iterator
class above each time it is exhausted.
So given a file hello.txt:
Hello world
Hola mundo
Guten tag, weld.
The classes can be used as followed:
iterator = Iterator('hello.txt')
for i in xrange(3):
print *** %d *** % i
for j in iterator:
print j
*** 0 ***
Hello wo
Hola mun
Guten ta
*** 1 ***
*** 2 ***
iterable = Iterable('hello.txt')
for i in xrange(3):
print *** %d *** % i
for j in iterable:
print j
*** 0 ***
Hello wo
Hola mun
Guten ta
*** 1 ***
Hello wo
Hola mun
Guten ta
*** 2 ***
Hello wo
Hola mun
Guten ta
When Iterator hits a StopIteration, it passes out of the inner loop, and
when it comes back in, the inner loop calls iterator.__iter__(), and
gets the same exhausted iterator (which immediately breaks the inner
loop by raising StopIteration). In Iterable, when the loop calls
iterable.__iter__(), it gets a fresh iterator, so it can loop over the
file again.
The important thing is that when you call x.__iter__() (which you do
when entering a loop), you get a fresh iterator that won't just call
StopIteration right away.
Cheers,
Cliff
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Re: Lambda alternative?
On Thu, 2009-04-16 at 13:33 +0200, Hrvoje Niksic wrote: mousemeat mousem...@gmail.com writes: Correct me if i am wrong, but i can pickle an object that contains a bound method (it's own bound method). No, you can't: import cPickle as p p.dumps([]) '(l.' p.dumps([].append) Traceback (most recent call last): File stdin, line 1, in module TypeError: expected string or Unicode object, NoneType found Yes he can. mousemeat stated that he could pickle an object that *contains* a bound method, not that he could pickle the method itself. That said, you can make an instance method out of a lambda, just as well as any named function, and you can pickle that object, too: Python 2.5.2 (r252:60911, Oct 5 2008, 19:29:17) [GCC 4.3.2] on linux2 Type help, copyright, credits or license for more information. import cPickle as p class Foo(object): ... a = lambda self, x: x+1 foo.a(1) 2 type(foo.a) type 'instancemethod' p.dumps(foo) 'ccopy_reg\n_reconstructor\np1\n(c__main__\nFoo\np2\nc__builtin__ \nobject\np3\nNtRp4\n.' Cheers, Cliff -- http://mail.python.org/mailman/listinfo/python-list
Re: [OT] large db question about no joins
On Thu, 2009-04-16 at 14:11 -0700, John Fabiani wrote: Daniel Fetchinson wrote: Hi folks, I've come across many times the claim that 'joins are bad' for large databases because they don't scale IMO that's bull... OK. That makes four legs so far -- http://mail.python.org/mailman/listinfo/python-list -- http://mail.python.org/mailman/listinfo/python-list
Re: extract Infobox contents
On Wed, 2009-04-08 at 01:57 +0100, Rhodri James wrote:
On Tue, 07 Apr 2009 12:46:18 +0100, J. Clifford Dyer
j...@sdf.lonestar.org wrote:
On Mon, 2009-04-06 at 23:41 +0100, Rhodri James wrote:
On Mon, 06 Apr 2009 23:12:14 +0100, Anish Chapagain
anishchapag...@gmail.com wrote:
Hi,
I was trying to extract wikipedia Infobox contents which is in format
like given below, from the opened URL page in Python.
{{ Infobox Software
| name = Bash
[snip]
| latest release date= {{release date|mf=yes|2009|02|20}}
| programming language = [[C (programming language)|C]]
| operating system = [[Cross-platform]]
| platform = [[GNU]]
| language = English, multilingual ([[gettext]])
| status = Active
[snip some more]
}} //upto this line
I need to extract all data between {{ Infobox ...to }}
[snip still more]
You end up with 'infoboxes' containing a list of all the infoboxes
on the page, each held as a list of the lines of their content.
For safety's sake you really should be using regular expressions
rather than 'startswith', but I leave that as an exercise for the
reader :-)
I agree that startswith isn't the right option, but for matching two
constant characters, I don't think re is necessary. I'd just do:
if '}}' in line:
pass
Then, as the saying goes, you only have one problem.
That would be the problem of matching lines like:
| latest release date= {{release date|mf=yes|2009|02|20}}
would it? :-)
That's the one.
A quick bit of timing suggests that:
if line.lstrip().startswith(}}):
pass
is what we actually want.
Indeed. Thanks.
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Re: Eval Problem
OK.
You still haven't shown the code where tableTop gets defined, so your
code is unrunnable. However, I think your problem is that wherever
tableTop lives, it isn't part of your globals or locals in eval. See
the documentation on evals here:
http://www.python.org/doc/1.4/lib/node26.html
Something like the following might work:
print eval(line, {'tableTop': tableTop})
Cheers,
Cliff
On Tue, 2009-04-07 at 08:38 -0400, Victor Subervi wrote:
I have excluded the code where I call the separate text files for
printing normal text. They work. It's my code that I cannot get to
work. For example, if I take out the eval part of the above, it will
nicely print the commands, such as this:
tableTop(123,456)
which is supposed to call said fn. If I place that line in the file
calling the text files and the bits file it will execute just fine,
but that inevitably makes my job harder. Ideas?
TIA,
Victor
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Re: Introducing Python to others
On Thu, 2009-03-26 at 09:35 +, Paddy O'Loughlin wrote: Hi, As our resident python advocate, I've been asked by my team leader to give a bit of a presentation as an introduction to python to the rest of our department. It'll be less than an hour, with time for taking questions at the end. There's not going to be a whole lot of structure to it. First, I'm going to open up a python terminal and show them how the interpreter works and a few basic syntax things and then a file .py files (got to show them that python's indenting structure is not something to be afraid of :P). I think I'll mostly show things in the order that they appear in the python tutorial (http://docs.python.org/tutorial/). My question to you, dear python-list, is what suggestions do you have for aspects of python that I should show them to make them maybe think that python is better than what they are using at the moment. All of the audience will be experienced (4+ years) programmers, almost all of them are PHP developers (2 others, plus myself, work in C, know C#, perl, java, etc.). Because of this, I was thinking of making sure I included exceptions and handling, the richness of the python library and a pointing out how many modules there were out there to do almost anything one could think of. Anything else you think could make PHP developers starting think that python is a better choice? If I were to do a (very) short demonstration one web framework for the PHP devs, what should I use? CherryPy (seems to be the easiest), Django (seems to be the biggest/most used), or something else? Any other suggestions for a possible wow reaction from an audience like that? 1) For PHP developers, I'm a big fan of clean namespaces. Show no code with `from foo import *`. Instead show them (using how by using `import foo` and `from foo import x, y, z`, your namespace only has those things you explicitly imported, plus the contents of `dir(__builtins__)`. 2) Aliasing imports is also cool. Show people how easy it is to switch from import MySQLdb as db to import psycopg2 as db and have all your dbapi2 code still work. Or from from StringIO import StringIO to from cStringIO import StringIO 3) Functions as first-class variables (which could connect to a discussion of decorators or of dictionaries as dispatch tables). 4) List comprehensions 5) Generators using yield 6) Also very handy is the interactive interpreter and the ability to type `dir(foo)` and `help(foo)` to see what facilities are available to you. Thanks, Paddy Cheers, Cliff -- http://mail.python.org/mailman/listinfo/python-list
Re: Mangle function name with decorator?
On Wed, 2009-03-18 at 08:18 -0700, Adam wrote:
On Mar 18, 10:33 am, J. Cliff Dyer j...@sdf.lonestar.org wrote:
You might be interested in redefining __getattribute__(self, attr) on
your class. This could operate in conjunction with the hash tables
(dictionaries) mentioned by andrew cooke. i.e. (untested code):
class C(object):
def __init__(self):
self._get_table = {}
self._post_table = {}
def __getattribute__(self, x):
if self.method=='GET':
return object.__getattribute__(self, _get_table)[x]
elif self.method=='POST':
return object.__getattribute__(self, _post_table)[x]
else:
raise AttributeError
@GET
def foo(x):
return Got, x
@POST
def foo(x)
return Posted to, x
This is definitely not functional code, but might get you in the right
direction on __getattribute__. __getattr__ might also work for you. I
haven't worked too much with these corners of python.
Cheers,
Cliff
Hey, Cliff. Thanks for sharing this idea. Unfortunately, providing a
way to actually call the method with the mangled name is relatively
easy, and there are options there. The real issue, to me, seems to be
finding a way to prevent Python from eating all but the last version
of a function definition in a class. While decorators are a elegant
and unintrusive approach, I don't believe that there is any way for a
decorator to collection information in a data structure and then
provide that data back to the class instance or the class's metaclass.
If your __getattribute__ dispatches method calls from a dictionary, it
shouldn't matter if the original name of the method has been blown away.
The actual method object lives on, and is accessed normally from the
user's standpoint.
I'm just thinking out loud now on ideas I haven't tested myself, but
what if your decorator were itself a method of the same class, so you
had something like this:
class BarBar(object):
def decorate_get(self, func):
pass
def decorate_post(self, func):
pass
@self.decorate_get
def foo(self):
pass
@self.decorate_post
def foo(self):
pass
Then the decorator has access to self, and can pass around whatever
information it needs. Maybe the decoration methods should live on a
base class somewhere.
class Decoratable(object):
def get(self, func):
pass
def post(self, func):
pass
class BarBar(Decoratable):
@self.get
def foo(self):
pass
@self.post
def foo(self)
pass
I'm beginning to think that I am trying to get the square peg of
Python to fit into the round hole of a .NET idiom.
Well, square is just one abstraction layer away from round anyway,
right?
I am trying to
borrow what I think is a really elegant and useful idiom from ASP.NET
MVC. Specifically, in an ASP.NET MVC Controller class, I can have two
methods with the same name that are called for different HTTP Verbs by
applying an Attribute:
public ActionResult Payment() {
ViewData[Title] = Payment Information;
ViewData[submit_text] = Next ;
return View();
}
[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Payment(FormCollection form) {
return RedirectToAction(Legal);
}
Right? The first Payment method is called when the Payment page is
rendered. The second is called when the form that it contains is
submitted. I find it to be readable, elegant and it does not intrude
into the actual logic of the method itself. The alternatives that I
can readily identify are less-than-optimal. For instance, if could
just have an if statement inside the body of the method that branches
on the HTTP verb:
def Payment(self):
if self.request.verb == 'GET':
# Do stuff for GET
elif self.request.verb == 'POST':
# So stuff for POST
Yes, it would work, but it is ugly and requires me to mix in the same
function the behaviors for two very separate things.
Or, I could do something like this:
def GET_Payment(self):
# Do stuff for GET
def POST_Payment(self):
# Do stuff for POST
This is trivially-easy to implement (in this case, a metaclass can
very easily manipulate the namespace), but it makes the source code
less appealing and just feels crufty and hacky. It also makes it
difficult to deal elegantly with having one method respond to more
than verb like I could if I could write:
@GET
@POST
def foo(self):
# Do stuff for page foo, if it is GET or POST; PUT and DELETE not
allowed!
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Re: Another of those is issues.
On Fri, 2009-03-20 at 11:20 -0700, Emanuele D'Arrigo wrote: Hi everybody, I was unit testing some code today and I eventually stumbled on one of those is issues quickly solved replacing the is with ==. Still, I don't quite see the sense of why these two cases are different: def aFunction(): ... pass ... f = aFunction f is aFunction True --- Ok, this seems reasonable. Nevertheless, I suspect I shouldn't quite rely on it. class MyClass(object): ... def myMethod(self): ... pass ... c = MyClass() m = c.myMethod m is c.myMethod False --- What? Why is that? In my mind I was expecting that when the method is assigned to m all that it happens is that its address is assigned to the name m so that effectively the same address is now pointed to by two names, like in the function case. I googled around for some hint but I wouldn't exactly say I'm clear on the issue just yet... Can anybody shed some light? Or point to a resource to look at? Or what's the bit of python's source code that is responsible for dealing with those assignments? Manu So here's a f'rinstance counterexample for you: class TempAttributeClass(object): def __init__(self): self.temp = True def foo(self, x): return len(x) + 1 def __getattribute__(self, attr): attribute = object.__getattribute__(self,attr) if hasattr(attribute, '__call__'): if object.__getattribute__(self, 'temp'): self.temp = False return len else: return attribute else: return attribute The first time a method is accessed from an instance of this class, it will return len instead. print TempAttributeClass.foo unbound method TempAttributeClass.foo c = TempAttributeClass() l = [1,2,3] x = c.foo x(l) 3 c.foo 4 x == c.foo False print x built-in function len print y bound method TempAttributeClass.foo of __main__.TempAttributeClass object at 0x7f672b35e290 c.foo is a bound attribute, but what has it been bound to? Well, I guess it technically, it's bound to the instance c, but what has it been bound from? That depends first on what it encounters when traversing its base classes, and second on how it's accessing its attributes. As the example above shows, python is too dynamic to make any guarantees about any of that. Another way you could mess with that is by changing the __class__ attribute on c. class A(object): x = 4 def __init__(self): self.y = 5 class B(object): x = u'cow' def __init__(self): self.y = u'goat' c = A() c.x 4 c.y 5 c.__class__ = B # Note that neither c nor x were changed in the last step ... c.x # Class attribute found on B now u'cow' c.y # Instance attribute: already initialized from A.__init__ 5 c.__init__() # Reinitialize c, now using B.__init__ c.y # Re-initialized instance attribute u'goat' Cheers, Cliff -- http://mail.python.org/mailman/listinfo/python-list
Re: Mangle function name with decorator?
You might be interested in redefining __getattribute__(self, attr) on
your class. This could operate in conjunction with the hash tables
(dictionaries) mentioned by andrew cooke. i.e. (untested code):
class C(object):
def __init__(self):
self._get_table = {}
self._post_table = {}
def __getattribute__(self, x):
if self.method=='GET':
return object.__getattribute__(self, _get_table)[x]
elif self.method=='POST':
return object.__getattribute__(self, _post_table)[x]
else:
raise AttributeError
@GET
def foo(x):
return Got, x
@POST
def foo(x)
return Posted to, x
This is definitely not functional code, but might get you in the right
direction on __getattribute__. __getattr__ might also work for you. I
haven't worked too much with these corners of python.
Cheers,
Cliff
On Tue, 2009-03-17 at 13:54 -0400, andrew cooke wrote:
ah, ok. then yes, you can do that with decorators. you'd need hash
tables or something similar in a metaclass. then the decorator would take
the given function, stick it in the appropriate hash table, and return a
function that does the dispatch (ie at run time does the lookup from the
hash table) (you'd only want to set the function once once, so it would
need to check the function wasn't already defined). also, the decorator
would have one name and get/post etc would be an argument.
this is all documented in the docs and peps, although it's very spread
around. you might look at the code for the property decorator - it's not
doing what you want, but it's an interesting non-trivial example that's
public.
http://docs.python.org/library/functions.html#property
andrew
Adam wrote:
Thanks, Andrew. I'm trying to accomplish something with a
metaprogramming flavor, where, for the convenience of the programmer
and the clarity of code, I'd like to have a decorator or some other
mechanism do twiddling behind the scenes to make a class do something
it wouldn't normally do.
Here's a less-obfuscated exmaple: I want to build a framework for
creating MVC web applications in Python (I know, I know, there's
already 2^1bazillion of them) where a controller class can have
methods that respond to the same action but for different HTTP verbs:
class foo_controller(Controller):
@GET
def new(self):
# Display the form to create a new foo
@POST
def new(self):
# Receive a form post with new foo data in it
The Controller class will do all of the work behind the scenes to
makes sure that the correct method is called at run-time, but for the
sake of the programmer, I'd like to supply a clear, friendly syntax
like this. Without a little metaprogramming magic, last-in-wins, and
only the second version of foo will end up in the class, so I'd like
to mangle the names to something that will result in a unique
attribute name and that the Controller class can work with behind the
scenes to do the right thing at run time.
So, Python experts, am I completely barking up the wrong tree here?
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Re: Battleship style game
On Wed, 2009-02-25 at 15:54 -0500, Shawn Milochik wrote: On Wed, Feb 25, 2009 at 3:15 PM, Diez B. Roggisch de...@nospam.web.de wrote: Not really. The point about properties is that you *can* make attribute access trigger getter or setter code. But not that you do unless there is an actual reason for that. The way you do it now is simply introducing clutter, without benefit. Your class would be half the current size - without loss of functionality. Diez -- http://mail.python.org/mailman/listinfo/python-list It is true that it would be fewer lines of code with the same functionality, but it's better practice to have that framework in place so that any changes made in the future wouldn't break any of the code accessing my class. Obviously this is a fairly simple game that has a fixed set of rules, but I'm trying to cultivate good habits, and I don't think that doing it this way is anti-Pythonic. Unless, of course, anything I said is wrong, which is always possible. If I'm missing a bigger-picture idea, I'd like to know about it. The piece you're missing is exactly why properties are so cool. They take what looks like attribute access from the client side, and pass it through a method. So while you can add any sort of changes you want to make can be made without breaking any client code. To them, it still looks like attribute access. class Foo(object): a = 4 class Bar(object): def __init__(self): self._a = 4 def _get_a(self): return self._a def _set_a(self, value): if not value % 2: self._a = value a = property(_get_a, _set_a) foo = Foo() foo.a 4 foo.a = 5 foo.a 5 bar = Bar() bar.a 4 bar.a = 5 bar.a 4 bar.a = 6 bar.a 6 Thanks, Shawn -- http://mail.python.org/mailman/listinfo/python-list -- http://mail.python.org/mailman/listinfo/python-list
Re: Is there something easier than ORM?
On Tue, 2009-02-17 at 06:15 -0800, 一首诗 wrote: Thanks for your reply. With sqlalchemy, an mapped must living in a session, you have no way to disconnect it with its session. For example : #- user = session.query(User).first() session.expunge(user) print user.name #Error here #- I just want to get an read-only copy of user disconnected with session to avoid unexpected database operation. But after expunge, properties of user is not accessible anymore. For that, the Right Thing to Do(tm) is to log in to your session with read-only permissions. -- http://mail.python.org/mailman/listinfo/python-list
Re: RedHat 4
It *works* in RHEL 4, but it doesn't come as a package. RHEL4 ships with Python 2.3, and RHEL 5 only ships with Python 2.4, even though 2.5 had been out for god knows how long when it came out. Though I haven't tested it, I wouldn't recommend replacing the system's python binary with 2.5 if you do install it yourself. Instead, install it to python2.5, and set the shebang line (#!) on your scripts to point to /usr/local/bin/python2.5 (or wherever you install it). Cheers, Cliff On Mon, 2009-02-16 at 07:28 -0800, Germán Gutiérrez wrote: Hi, I need to confirm and certificate python 2.5 works in a RedHat Enterprise 4 and I don't know where I find that information. Please, if anybody knows some URL in RedHat or Python with this information email me. Thanks Germán Gutiérrez Gayoso Temuco -- http://mail.python.org/mailman/listinfo/python-list -- http://mail.python.org/mailman/listinfo/python-list
Re: Pythonic way to determine if one char of many in a string
On Mon, 2009-02-16 at 00:28 -0500, Nicolas Dandrimont wrote:
* pyt...@bdurham.com pyt...@bdurham.com [2009-02-16 00:17:37 -0500]:
I need to test strings to determine if one of a list of chars is
in the string. A simple example would be to test strings to
determine if they have a vowel (aeiouAEIOU) present.
I was hopeful that there was a built-in method that operated
similar to startswith where I could pass a tuple of chars to be
tested, but I could not find such a method.
Which of the following techniques is most Pythonic or are there
better ways to perform this type of match?
# long and hard coded but short circuits as soon as match found
if 'a' in word or 'e' in word or 'i' in word or 'u' in word or
... :
-OR-
# flexible, but no short circuit on first match
if [ char for char in word if char in 'aeiouAEIOU' ]:
-OR-
# flexible, but no short circuit on first match
if set( word ).intersection( 'aeiouAEIOU' ):
I would go for something like:
for char in word:
if char in 'aeiouAEIUO':
char_found = True
break
else:
char_found = False
(No, I did not forget to indent the else statement, see
http://docs.python.org/reference/compound_stmts.html#for)
It is clear (imo), and it is seems to be the intended idiom for a search
loop, that short-circuits as soon as a match is found.
If performance becomes an issue, you can tune this very easily, so it
doesn't have to scan through the string 'aeiouAEIOU' every time, by
making a set out of that:
vowels = set('aeiouAEIOU')
for char in word
if char in vowels:
return True
return False
Searching in a set runs in constant time.
Cheers,
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Re: wxPython and Croatian characters
On Mon, 2009-02-16 at 20:06 +0100, Diez B. Roggisch wrote:
vedrandeko...@gmail.com schrieb:
Hello,
I have problem with configuring my wxPython script to work with
Croatian characters like: đ,š,ž,č,ć.
Here is my simple script without wxPython (this script works):
# -*- coding: utf-8 -*-
s = hello normal string đšžćč
print s
..here is my snippet with wxPython:
text = wx.StaticText(self, -1,Matični broj,(0,100)) # in this
example,we have character č
...when I run this text, it looks something like: Mati,some weird
characters ,and ni
Unless you are using python 3.0 (which I doubt, afaik no wx available),
your above coding declaration is useless for the shown piece of code, as
it only applies to unicode literals, which are written with a preceding u.
No. The coding declaration does nothing to unicode literals. It only
affects how the python's source code parser reads the the source code.
Without it, your source code will be parsed (or is it lexed?) by python
as an ascii document. So if your document is UTF-8, it will choke as
soon as it reaches a non ascii character. If it's encoded in UTF-16,
however, it will choke right away, as it will immediately come across a
\x00 byte, which is treated as the ascii NULL character, which is not
legal in python source code.
But print will still try to encode all unicode objects to the encoding
of your terminal, and any file writing operations will try to decode as
ASCII, unless explicitly told otherwise. Same as without the -*- coding
-*- declaration.
For the OP:
When dealing with potentially non-ascii text, always use unicode objects
instead of strings, and explicitly encode them to the encoding you want
on output, unless your printing facility (here wx.StaticText) handles
that for you. I also don't know how wxpython works in this regard.
So:
s = uMatični broj # instead of Matični broj
text = wx.StaticText(self, -1, s,(0,100))
# or if that doesn't work try this:
#text = wx.StaticText(self, -1, s.encode('utf-8'), (0,100))
Cheers,
Cliff
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Re: English-like Python
On Thu, 2009-01-22 at 09:07 -0700, Joe Strout wrote: Beep Doesn't get much more readable and syntax-free than that. readable doesn't mean smallest amount of syntax possible sometimes syntax increases the readability of a text as you would see if we for example dropped all punctuation but you probably already knew that but perhaps you didnt draw the connection with programming language wink Cute. But I stand by my contention that Beep is about the most readable way imaginable to express the make a beep sound now please command, and any additional punctuation (parentheses, semicolons, etc.) only get in the way. But what if your language allows functions to be used as first class objects? (Mine does :)) x = Beep Does that assign the name x to the Beep object or does it assign the result of a Beep call to x? There's no virtue in making ridiculously simple things even simpler if it makes the interesting things impossible. def tone_sequence(sound): sequence = DialTone.followed_by(sound) sequence() for x in Beep, Buzz, Warble: tone_sequence(x) Cheers, Cliff -- http://mail.python.org/mailman/listinfo/python-list
Re: English-like Python
On Tue, 2009-02-03 at 08:33 -0700, Joe Strout wrote: J. Cliff Dyer wrote: But what if your language allows functions to be used as first class objects? (Mine does :)) x = Beep Does that assign the name x to the Beep object or does it assign the result of a Beep call to x? It assigns the result. To assign the name to the Beep object requires a bit of additional syntax; in RB, this would be x = AddressOf Beep There's no virtue in making ridiculously simple things even simpler if it makes the interesting things impossible. Of course. The goal is (or should be) to make the common things ridiculously simple, and make the uncommon things only somewhat less so. Even in Python, it is far more common to invoke a function than to need a reference to it. So invoking a function should be the thing that requires no extra syntax (even including ()). Getting a reference to it, which is less common, should be the thing that requires more syntax. Except that now you have introduced an inconsistency into python. What does the following mean? my_object = MyObject() x = my_object What if MyObject defines a method named __call__? Now some objects are passed around using x = my_object while others require x = AddressOf my_object and the only way to tell which is which is to check the object for the presence of a __call__ method. This seems like a serious inconsistency to me. Cheers, - Joe Cliff -- http://mail.python.org/mailman/listinfo/python-list
Re: var is None vs. var == None
On Fri, 2009-01-23 at 19:31 -0500, Benjamin Kaplan wrote: On Fri, Jan 23, 2009 at 7:28 PM, Gary Herron gher...@islandtraining.com wrote: Steven D'Aprano wrote: On Fri, 23 Jan 2009 14:58:34 -0500, Gerald Britton wrote: Hi -- Some time ago I ran across a comment recommending using var is None instead of var == None (also var is not None, etc.) That entirely depends on whether you wish to test for something which *is* None or something with *equals* None. Those two things have different meanings. Actually, for None, those two things *are* the same. If something *equals* None, it also *is* None. This is a consequence of the fact that there is only ever one value of None anywhere in the system. Not if someone decided to be a PITA. class A(object) : ...def __eq__(self, other) : ... return other is None ... a = A() a == None True a is None False or slightly less PITAish: class EqualThing(object): def __eq__(self, other): return True Could be a useful sentinel value in some cases. I wonder, do newbies actually get the impression from somewhere that is is a synonym for ==? Yes. Such questions pop up regularly, and are usually dealt with quickly. My own testing indicates that the former beats the latter by about 30% on average. Not a log for a single instruction but it can add up in large projects. If you have a large project where the time taken to do comparisons to None is a significant portion of the total time, I'd be very surprised. var is None is a micro-optimization, but that's not why we do it. We do it because usually the correct test is whether var *is* None and not merely equal to None. Any random object might happen to equal None (admittedly most objects don't), but only None is None. You don't have that quite right. The only way something can *equal* None is if it *is* None. None is not a value an object can have, but rather it is a (singleton) object that can be referenced. Setting something *equal* to None is accomplished by making it refer to the single None object, at which point it *is* None. Gary Herron -- http://mail.python.org/mailman/listinfo/python-list -- http://mail.python.org/mailman/listinfo/python-list -- http://mail.python.org/mailman/listinfo/python-list
Re: v = json.loads({'test':'test'})
On Sun, 2009-01-25 at 14:28 -0800, gert wrote:
On Jan 25, 11:16 pm, Дамјан Георгиевски gdam...@gmail.com wrote:
raise ValueError(errmsg(Expecting property name, s, end))
http://docs.python.org/library/json.html
What am I doing wrong ?
try this
v = json.loads('{test:test}')
JSON doesn't support single quotes, only double quotes.
the funny part is when you print(v) you get
{'test': 'test'}
Single quotes works in every browser that support json so i
recommended python should support it too, besides it looks much
cleaner
{'test': 'test'}
{test: test}
It can not be that hard to support both notation can it ?
It's not that hard, but it does add a noticeable level of complexity to
the process. In JSON, you simply tell the parser, if you see a
double-quote character, we're now parsing a string. When you see
another (unescaped) double-quote character, the string is done.
The equivalent version for your extended JSON would say, if you see a
quote character of either kind, we're parsing a string. When you see
another (unescaped) quote character of either kind, the string is done.
But that doesn't work, because it would allow {'test: test'}. So the
parser has to remember which quote character is being used, and require
those characters to be escaped, and not the other (but then does te
\'st render as rte'st or rte\'st?) and only close the string when
the appropriate quote is found.
Not an impossible task, but certainly more complex than the current
parsing requirements for JSON.
Cheers,
Cliff
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Re: Newby: how to transform text into lines of text
On Sun, 2009-01-25 at 18:23 -0800, John Machin wrote:
On Jan 26, 1:03 pm, Gabriel Genellina gagsl-...@yahoo.com.ar
wrote:
En Sun, 25 Jan 2009 23:30:33 -0200, Tim Chase
python.l...@tim.thechases.com escribió:
Unfortunately, a raw rstrip() eats other whitespace that may be
important. I frequently get tab-delimited files, using the following
pseudo-code:
def clean_line(line):
return line.rstrip('\r\n').split('\t')
f = file('customer_x.txt')
headers = clean_line(f.next())
for line in f:
field1, field2, field3 = clean_line(line)
do_stuff()
if field3 is empty in the source-file, using rstrip(None) as you suggest
triggers errors on the tuple assignment because it eats the tab that
defined it.
I suppose if I were really smart, I'd dig a little deeper in the CSV
module to sniff out the right way to parse tab-delimited files.
It's so easy that don't doing that is just inexcusable lazyness :)
Your own example, written using the csv module:
import csv
f = csv.reader(open('customer_x.txt','rb'), delimiter='\t')
headers = f.next()
for line in f:
field1, field2, field3 = line
do_stuff()
And where in all of that do you recommend that .decode(some_encoding)
be inserted?
If encoding is an issue for your application, then I'd recommend you use
codecs.open('customer_x.txt', 'rb', encoding='ebcdic') instead of open()
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Re: I'm a python addict !
On Mon, 2009-01-26 at 14:43 -0800, J Kenneth King wrote: Linuxguy123 linuxguy...@gmail.com writes: I just started using python last week and I'm addicted. I hate Perl. I never did learn to use it with any competence. I has to be the most obfuscated, cryptic language I've ever seen. Making it object oriented only makes it worse ! .. snip .. I program full-time in Python, so I share your excitement and enthusiasm. But bashing Perl like that doesn't make you sound very smart. I'm probably one of the very few Python programmers who came from (and still occassionally) use Perl. Really? I think many many python programmers cut their teeth on Perl. I for one. I loved programming in it when I did, but I hate having to try to understand OPP. Now, when I deal with Perl, it's mostly legacy code, and it's a miserable experience. I've written non-trivial programs in it and from my experience I can tell you that it's actually a great language. The Moose object system is well beyond Python's class system. But I guess you wouldn't know that. So yay for Python, but don't get in the habit of criticising that which you do not know. There are legitimate reasons to criticize things even when they are powerful. Cheers, Cliff -- http://mail.python.org/mailman/listinfo/python-list
Re: I'm a python addict !
On Fri, 2009-01-23 at 20:25 -0800, Paul McGuire wrote: Want to change the type/behavior of an object from class A to class B? How about this: aobj = A() aobj.__class__ = B Try *that* in as simple-looking C++ or Java! Wow. That looks very powerful and fun. But scary. Any thoughts on how you would use that in a way that wouldn't unleash sulphurous code smells? Cheers, Cliff -- http://mail.python.org/mailman/listinfo/python-list
Re: I'm a python addict !
On Mon, 2009-01-26 at 09:52 -0800, Paul McGuire wrote: On Jan 26, 10:54 am, J. Cliff Dyer j...@sdf.lonestar.org wrote: On Fri, 2009-01-23 at 20:25 -0800, Paul McGuire wrote: Want to change the type/behavior of an object from class A to class B? How about this: aobj = A() aobj.__class__ = B Try *that* in as simple-looking C++ or Java! Wow. That looks very powerful and fun. But scary. Any thoughts on how you would use that in a way that wouldn't unleash sulphurous code smells? This technique is perfect for implementing the GoF State pattern. In the State pattern, you implement behavior for an object's various states using one of several interchangeable classes. The classes are interchangeable in that they all implement a common interface. Here is my favorite State pattern example, a traffic light: import time class TrafficLight(object): pass class RedLight(TrafficLight): cars_can_go = False pedestrians_can_cross = True color = (255,0,0) duration = 20 class YellowLight(TrafficLight): cars_can_go = True pedestrians_can_cross = False color = (255,255,0) duration = 5 class GreenLight(TrafficLight): cars_can_go = True pedestrians_can_cross = False color = (0,255,0) duration = 15 # now add in next_state class vars for state transitions RedLight.next_state = GreenLight YellowLight.next_state = RedLight GreenLight.next_state = YellowLight TrafficLight.initial_state = RedLight # run a traffic light for a while... can_they = lambda cond : (can't,can)[cond] light = TrafficLight.initial_state() while 1: print light.__class__.__name__ print waiting for, light.duration, seconds print Cars, can_they(light.cars_can_go), go print People, can_they(light.pedestrians_can_cross), cross print time.sleep(light.duration) # how you have to do it in C++ and Java # light = light.next_state() # using Python light.__class__ = light.next_state Gives this output: RedLight waiting for 20 seconds Cars can't go People can cross GreenLight waiting for 15 seconds Cars can go People can't cross YellowLight waiting for 5 seconds Cars can't go People can't cross RedLight waiting for 20 seconds Cars can't go People can cross ... and so on ... In Python, the base TrafficLight class isn't even necessary (don't need no stinking interfaces!), although it is a good place to define default behavior, and it helps tie together the other classes from a self-documentation standpoint. But any class that has the necessary attributes would suffice, whether it inherits from TrafficLight or not. class HoldForEmergencyVehiclesLight(object): cars_can_go = False pedestrians_can_cross = False color = (255,0,0) -- Paul Thanks. That makes sense. But your example creates a new instance of the new class each time, rather than changing the class of a persistent instance, as the original example, to which I was responding, did. But perhaps something like: class TrafficLight(object): def change_light(self): self.__class__ = next_state and then you can persist information about the light (bulb_type in set(['led', 'incandescent']), last_maintenance_date, location, etc.) on the instance level, unaffected by the changing color. Interesting stuff. Cheers, Cliff -- http://mail.python.org/mailman/listinfo/python-list
Re: I'm a python addict !
On Mon, 2009-01-26 at 12:37 -0800, Paul McGuire wrote: On Jan 26, 2:06 pm, J. Cliff Dyer j...@sdf.lonestar.org wrote: Thanks. That makes sense. But your example creates a new instance of the new class each time, rather than changing the class of a persistent instance, as the original example, to which I was responding, did. Look closer. The line that creates a new instance is commented out, with the notation how you have to do it in C++ and Java. The actual Python code is just below, and just assigns a new class to self.__class__, as in the original example. Right. Sorry about that. -- Paul -- http://mail.python.org/mailman/listinfo/python-list -- http://mail.python.org/mailman/listinfo/python-list
Re: The First Law Of comp.lang.python Dynamics
I dub it Schluehr's law. On Thu, 2009-01-22 at 21:39 -0800, Kay Schluehr wrote: Whatever sufficiently sophisticated topic was the initially discussed it ends all up in a request for removing reference counting and the GIL. -- http://mail.python.org/mailman/listinfo/python-list -- http://mail.python.org/mailman/listinfo/python-list
Skull Socks (was Re: Convention vs. fascism)
On Fri, 2009-01-16 at 08:57 +, Steven D'Aprano wrote: On Fri, 16 Jan 2009 10:03:28 +0200, Hendrik van Rooyen wrote: Oh come on you lot - you are carrying on as if Diez were wearing his skull socks again - do me a favour and give him a break! And... skull socks? Cool. Where can I get some? http://www.letmegooglethatforyou.com/search?q=skull+socks -- http://mail.python.org/mailman/listinfo/python-list
Re: Creating new instances of subclasses.
Thanks for the solutions everyone! I'm not sure which I'll end up
using, but I think I've got a better grasp of the problem now.
Cool stuff.
Cheers,
Cliff
On Thu, 2009-01-08 at 06:52 -0800, Paul McGuire wrote:
On Jan 7, 12:00 pm, Paul McGuire pt...@austin.rr.com wrote:
On Jan 7, 10:38 am, J. Cliff Dyer j...@unc.edu wrote:
I want to be able to create an object of a certain subclass, depending
on the argument given to the class constructor.
I have three fields, and one might need to be a StringField, one an
IntegerField, and the last a ListField. But I'd like my class to
delegate to the proper subclass automatically, so I can just do:
f1 = Field('abc')
f2 = Field('123')
f3 = Field('D,E,F')
O-O is not always the solution to every problem. Since inheritance is
getting in your way, try using a class-level factory method. Instead
of using the Field constructor, use a staticmethod of Field, something
like:
@staticmethod
def make_Field(a)
if is_list(a):
return ListField(a)
elif is_integer(a):
return IntegerField(a)
else:
return StringField(a)
and then get rid of all those __new__ methods, too.
-- Paul
After looking this over a bit more, I decided I didn't like make_Field
having to know the criteria for creating the different subclasses, but
wanted to put the smarts into the subclasses themselves. Here is an
excerpt that shows this working:
class Field(object):
def __init__(self, input):
super(Field, self).__init__(input)
self.data = input
@staticmethod
def make_Field(a):
subs = (ListField, IntegerField, StringField)
ret = None
for cls in subs:
try:
ret = cls(a)
except TypeError:
continue
else:
break
return ret
class IntegerField(Field):
def __new__(cls, a):
if not is_integer(a):
raise TypeError()
return Field.__new__(cls, a)
...
ListField has a similar __new__ method, and StringField just creates
the object, with no validation.
make_Field still has to know what order to list the subclasses in
(StringField is the most permissive, and so must come last in the list
of subclasses), but the specific type tests are moved into the
subclasses, which is a more appropriate place I think.
-- Paul
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Re: Problem with -3 switch
On Fri, 2009-01-09 at 13:13 -0500, Steve Holden wrote: Aivar Annamaa wrote: As was recently pointed out in a nearly identical thread, the -3 switch only points out problems that the 2to3 converter tool can't automatically fix. Changing print to print() on the other hand is easily fixed by 2to3. Cheers, Chris I see. So i gotta keep my own discipline with print() then :) Only if you don't want to run your 2.x code through 2to3 before you use it as Python 3.x code. regards Steve And mind you, if you follow that route, you are programming in a mightily crippled language. It's about as bad as trying to write cross-browser CSS. Don't put yourself through that pain if you don't have to. -- http://mail.python.org/mailman/listinfo/python-list
Creating new instances of subclasses.
I want to be able to create an object of a certain subclass, depending
on the argument given to the class constructor.
I have three fields, and one might need to be a StringField, one an
IntegerField, and the last a ListField. But I'd like my class to
delegate to the proper subclass automatically, so I can just do:
f1 = Field('abc')
f2 = Field('123')
f3 = Field('D,E,F')
f1.data
'abc'
f2.data
123
f3.data
['D','E','F']
type(f1)
class '__main__.StringField'
type(f2)
class '__main__.StringField'
type(f3)
class '__main__.ListField'
I've come up with a solution, but I suspect there's something cleaner I
can do with the inheritance structure of __new__. I don't like
explicitly leapfrogging over Field.__new__ to object.__new__.
My attempt is below:
def is_list(arg):
if ',' in arg: return True
else: return False
def is_integer(arg):
try: int(arg)
except ValueError: return False
else: return True
class Field(object):
def __new__(cls, a):
if is_list(a):
return ListField(a)
elif is_integer(a):
return IntegerField(a)
else:
return StringField(a)
def __init__(self, input):
super(Field, self).__init__(input)
self.data = input
class IntegerField(Field):
def __new__(cls, a):
return object.__new__(cls, a)
def __init__(self, s):
super(IntegerField, self).__init__(s)
self.s = int(self.s)
class ListField(Field):
def __new__(cls, a):
return object.__new__(cls, a)
def __init__(self, s):
super(ListField, self).__init__(s)
self.s = s.split(',')
class StringField(Field):
def __new__(cls, a):
return object.__new__(cls, a)
Is there a cleaner way to do this? The main problem is that
Field.__new__ gets in the way of properly constructing the subclasses
once I've used it to select the proper subclass in the first place.
Cheers,
Cliff
--
Oook,
J. Cliff Dyer
Carolina Digital Library and Archives
UNC Chapel Hill
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Re: python is great
On Tue, 2009-01-06 at 10:36 -0700, Joe Strout wrote: I've actually been rather frustrated by Python lately. OFF TOPIC!!! Please try to stay within the subject presented by the subject header. The subject in question is python is great, not python is frustrating. Speaking of which, python is truly great. -- http://mail.python.org/mailman/listinfo/python-list
Re: subclassing 'list'
On Tue, 2009-01-06 at 12:34 -0800, akineko wrote:
Hello everyone,
I'm creating a class which is subclassed from list (Bulit-in type).
It works great.
However, I'm having a hard time finding a way to set a new value to
the object (within the class).
There are methods that alter a part of the object (ex. __setitem__()).
But I couldn't find any method that can replace the value of the
object.
I wanted to do something like the following:
class Mylist(list):
def arrange(self):
new_value =
list.self.__assign__.(self, new_value)
I serached the newsgroup and found that assignment operator ('=')
cannot be overridden because it is not an operator. But it shouldn't
stop Python to provide a way to re-assign the value internally.
Aki,
I'm not sure I understand your problem. What I see above is an
attribute error:
AttributeError: type object 'list' has no attribute 'self'
coming from your use of list.self, but it doesn't sound like that's what
you are asking about. Do you mean that you want to be able to specify
some sort of processing to be done when you assign to an attribute of
your object? To do that, you need to use properties:
import math
class Circle(object):
def __init__(self, radius=1.0):
self._radius = radius
self.circum = 2.0 * self._radius * math.pi
def __get_radius(self):
return self._radius
def __set_radius(self,radius):
self._radius = radius
self.circum = 2.0 * self._radius * math.pi
radius = property(__get_radius, __set_radius)
Then you can do:
circ = Circle(2.0)
print circ.radius
2.0
print circ.circum
12.5663706144
circ.radius = 4.5
print circ.radius
4.5
print circ.circum
28.2743338823
There are lots of good tutorials on this online.
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Re: __init__.py and package help
On Mon, 2009-01-05 at 11:49 -0800, TechieInsights wrote:
Ok I have read all of the tutorials and documents I could find. I am
running Python 2.6 on windows. The problem I am having with packages
is that they don't show up!
Simple example of what isn't working...
Structure-
pytest/ Root directory of package
__init__.py- code: __all__ = ['folder']
folder/ Another folder in the package
__init__.py- code: __all__ = ['hello']
hello.py- code: print('Hello World')
Then I append the path to sys.path, and try and import...
sys.path.append(r'E:\dev\test\pytest')
from pytest.folder import hello
Traceback (most recent call last):
File stdin, line 1, in module
ImportError: No module named pytest.folder
What am I doing wrong! It's driving me crazy.
Thanks in advance,
Greg
You want
sys.path.append(r'E:\dev\test')
unless your code is in E:\dev\test\pytest\pytest\folder\hello.py
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Re: help I'm getting delimited
On Wed, 2008-12-17 at 06:28 -0800, aka wrote: Hi John, thanks. You're right, I didn't past the method header because I thought it didn't matter when the input filename is hardcoded. The try/except isn't very helpful indeed so I commented it out. You're right I wrongly referred to the UnicodeReader class in my first post because that's ultimately where I want to go so I outcommented it here for you to see. The fact is that neither csv.reader nor the UnicodeReader will read the file, while writing with the UnicodeWriter works like a charm. That's why I put str() around roles to see any content. I simplified the csv-file by cutting off columns without result. The file looks now like: id;company;department 12;Cadillac;Research 11;Ford;Accounting 10;Chrysler;Sales The dictionary on the return is because this code is part of my TurboGears application. The entire method is: import csv from utilities.urw import UnicodeWriter, UnicodeReader @expose(allow_json=True) def import_roles(self, input=None, *args, **kwargs): inp = 'C:/temp/test.csv' roles = [] msg = '' ## try: fp = open(inp, 'rb') reader = csv.reader(fp, dialect='excel', delimiter=';') ## reader = UnicodeReader(fp, dialect='excel', delimiter=';') for r in reader: roles.append(r[0]) fp.close() ## except: ## msg = Something's wrong with the csv.reader return dict(filepath=inp, roles=str(roles), msg=msg) csv.reader results in: for r in reader: Error: line contains NULL byte Use of UnicodeReader results in: UnicodeDecodeError: 'utf8' codec can't decode byte 0xff in position 0: unexpected code byte This looks like the problem might be in your choice of codec. A UTF-8 file will never have 0xff in it, and would be unlikely to have 0x00 either. My guess is that you will need to decode your input from UTF-16. (and then use the UnicodeReader). Will post only complete code from now on thanks. -- http://mail.python.org/mailman/listinfo/python-list -- http://mail.python.org/mailman/listinfo/python-list
Re: Factoring Polynomials
On Thu, 2008-12-18 at 11:52 -0800, eric wrote: On Dec 18, 8:37 pm, collin.da...@gmail.com wrote: I am trying to write a simple application to factor polynomials. I wrote (simple) raw_input lines to collect the a, b, and c values from the user, but I dont know how to implement the quadratic equation x = (-b +or- (b^2 - 4ac)^1/2) / 2a into python. Any ideas? with numpy: from numpy import * s=[1,-1] x = -b+s*sqrt( b**2-4*a*c )/(2*a) Eric Without the Nump. def polynomial(a, b, c): N = ((b**2 - 4*a*c)**.5) / 2*a return (-b + N, -b - N) -- http://mail.python.org/mailman/listinfo/python-list
