count strangeness
tal 65% python2.7 Python 2.7.1 (r271:86832, May 21 2011, 22:52:14) [GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin Type help, copyright, credits or license for more information. py class C(object): ... def __init__(self): ... self.data = [] ... def doit(self, count=0): ... for c in self.data: ... count += c.doit(count) ... count += 1 ... print count ... return count ... py c = C() py c.data.extend([C() for i in xrange(10)]) py c.doit() 1 2 4 8 16 32 64 128 256 512 1024 1024 WTF? James -- http://mail.python.org/mailman/listinfo/python-list
Re: count strangeness
Chris Rebert wrote: WTF? Assuming your question is Why is 1024 there twice?, the answer is The question is Why is 1024 there at all? It should be 10. James -- http://mail.python.org/mailman/listinfo/python-list
Re: count strangeness
Peter Otten wrote: James Stroud wrote: WTF? Put the code into a file, run it -- and be enlightened ;) tal 72% python2.7 eraseme.py 1 2 4 8tal 73% cat eraseme.py #! /usr/bin/env python class C: def __init__(self): self.data = [] def doit(self, count=0): for c in self.data: count += c.doit(count) count += 1 print count return count c = C() c.data.extend([C() for i in xrange(10)]) c.doit() tal 74% python2.7 eraseme.py 1 2 4 8 16 32 64 128 256 512 1024 Hmmm. It's still 1024. What am I missing? James -- http://mail.python.org/mailman/listinfo/python-list
Re: count strangeness
James Stroud wrote: Chris Rebert wrote: WTF? Assuming your question is Why is 1024 there twice?, the answer is The question is Why is 1024 there at all? It should be 10. James I mean 11, not 10--but you get the point. James -- http://mail.python.org/mailman/listinfo/python-list
Re: count strangeness
Peter Otten wrote: James Stroud wrote: WTF? Put the code into a file, run it -- and be enlightened ;) Compare the follower to the last. tal 77% cat eraseme.py #! /usr/bin/env python class C: def __init__(self): self.data = [] def doit(self, count=[0]): for c in self.data: c.doit() count[0] += 1 print count[0] c = C() c.data.extend([C() for i in xrange(10)]) c.doit() tal 78% python2.7 eraseme.py 1 2 3 4 5 6 7 8 9 10 11 James -- http://mail.python.org/mailman/listinfo/python-list
Re: count strangeness
Chris Rebert wrote: On Sat, May 21, 2011 at 11:32 PM, James Stroud jstr...@mbi.ucla.edu wrote: Chris Rebert wrote: WTF? Assuming your question is Why is 1024 there twice?, the answer is The question is Why is 1024 there at all? It should be 10. Ah. This is why it's better to be more explicit about what your question is than a mere WTF?. In that case, I believe you meant to write: count += c.doit() rather than: count += c.doit(count) I get it. Thank you. James -- http://mail.python.org/mailman/listinfo/python-list
Re: Regex driving me crazy...
Patrick Maupin wrote:
BTW, although I find it annoying when people say don't do that when
that is a perfectly good thing to do, and although I also find it
annoying when people tell you what not to do without telling you what
*to* do, and although I find the regex solution to this problem to be
quite clean, the equivalent non-regex solution is not terrible
I propose a new way to answer questions on c.l.python that will (1) give
respondents the pleasure of vague admonishment and (2) actually answer the
question. The way I propose utilizes the double negative. For example:
You are doing it wrong! Don't not do codere.split('\s{2,}', s[2])/code.
Please answer this way in the future.
Thank you,
James
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s-expression parser in python
Hello All, I want to use an s-expression based configuration file format for a python program I'm writing. Does anyone have a favorite parser? I'm currently using sexpy.parse() (http://pypi.python.org/pypi/sexpy) which works very well but I don't know how secure it is. Does anyone have experience with sexpy or another parser? I'm mostly concerned with safety when the parser evaluates scalar data types. Sexpy is not well documented in this regard. Also, I don't want a lisp/scheme interpreter, just the parser. For example, (and (or ( uid 1000) (!= gid 20) ) ( quota 5.0e+03) ) Should be parsed to [and, [or, [=, uid, 1405], [!=, gid, 20]], [, quota, 5000.0] ] Note proper parsing of ints, floats, etc. I've already wrote the evaluator for the parsed lists, so I'm not interested in alternatives to S-expressions. Also, I'm really not interested in json, yaml, etc., for the configuration format because I'm quite fond of the brevity and clarity of S-expressions (your opinion may vary). Thanks in advance for any insight. James -- http://mail.python.org/mailman/listinfo/python-list
Re: python as pen and paper substitute
Manuel Graune wrote: Hello everyone, I am looking for ways to use a python file as a substitute for simple pen and paper calculations. At the moment I mainly use a combination of triple-quoted strings, exec and print (Yes, I know it's not exactly elegant). To clarify, I just start an editor, write a file that might look something like this: I wrote a module called pylave, which is meant to be a parser-evaluator-solver for scratch paper-like calculations. It has strict operator precedence, knows a variety of common operations, and respects parenthetic grouping. It is designed to evaluate ini files, which can have syntax highlighting depending on your text editor. Pyparsing is required. Here is a pylave example: % cat test.ini factor = 2 = minor_axis / 2 www= 69.69 + height = 10 apex = epicenter // height major_axis = epicenter + 2*radius / sin big minor_axis = epicenter + (total / 14) % (length-1) epicenter = 44 radius = ((14 + length)/2 + height)*breadth length = width + 5 width = 2**2 - factor total = big*(radius + 14) big= abs (sin (5e+8)) breadth= 2*length + height overlap= abs (1 + 1) nexus = sin (5e-8) plexus = sin (5e8) % ./pylave.py test.ini breadth : 24 www : 93.8350093235 nexus : 5e-08 big : 0.284704073238 major_axis : 3547.35712408 height : 10 radius : 492.0 plexus : -0.284704073238 total : 144.060261058 epicenter : 44 apex : 4 overlap : 2 : 24.1450093235 width : 2 length : 7 factor : 2 minor_axis : 48.290018647 It is not perfect but if it will help, I'll cheeseshop it. James -- http://mail.python.org/mailman/listinfo/python-list
Re: Frustrated with scopes
James Stroud wrote: def stream_factory: class Line(object): __source = source __join = join # etc. return Line of course I meant def stream_factory(lines, source, join=''.join): James -- http://mail.python.org/mailman/listinfo/python-list
Re: hashability
Asun Friere wrote:
On Aug 12, 3:32 pm, James Stroud nospamjstroudmap...@mbi.ucla.edu
wrote:
You should be more imaginative.
I'm by no means discounting that there might be some actual problem
you're trying to solve here, but I honestly can't see it.
There really is no need to get personal about this, so rather than
asking for a level of imagination from me, (which I apparently lack),
please just explain to me how {one_instance_of_a_hashable_class : val,
another_instance_of_a_hashable_class :val} is conceptually different
{one_instance_of_class_str: val, another_instance_of_class_str: val},
in terms of persistence.
Sorry for being a twit. This list used to be quite nice but some people
on this list got pretty abrasive. I couldn't tell you weren't one of
these abrasive people from your post. I stopped giving the benefit of
the doubt many moons ago and promptly enter attack mode at the slightest
hint of abrasiveness. My attitude probably exacerbates the problem--but
it sure does make me feel better.
Anyway, I think the problem has been described better than I'm able, but
once an object goes to the file system, one can not take its hash value
for granted. It is not possible to rely on the ability to recreate any
arbitrary object de-novo and use the recreation as a key in proxy for
the original object. I'm after this je ne sais pas que l'appeler
quality of objects to use as keys (or to generate keys) for persistent
dictionaries. Carl Banks suggested that this quality should not be
called hashable, so I'm calling it keyable.
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Re: hashability
Dennis Lee Bieber wrote:
On Tue, 11 Aug 2009 17:54:36 -0700, James Stroud jstr...@mbi.ucla.edu
declaimed the following in gmane.comp.python.general:
...
py {C():4}[C()]
Traceback (most recent call last):
File ipython console, line 1, in module
type 'exceptions.KeyError': __main__.C object at 0xe21610
The basis for the exception is that the two instances do not have the
same hash() although conceptually they might seem equal to the
unitiated. Were I to re-design python, I'd throw an exception in this
case because of the ill-defined behavior one might expect if a C()
serves as a key for a dict.
A C()... How would you expect
c1 = C()
c2 = C()
{c1:4}[c2]
to behave?
This seems like a subjective question. I think I demonstrated how it
*does* behave, which is purely objective--and I know I can't do anything
about that. But the subjective answer to the subjective question is that
I would like an exception to be raised when the dictionary is
constructed. I know an exception doesn't get thrown in the current
incarnation of the python language. That is the objective reality of the
situation which affronts my subjective notions of how reality should be.
That IS the equivalent of your statement -- two instances are
two distinctly different entities...
Tell that to two different machines on two different days. Then bet the
life of yourself and your nearest and dearest family on that fact and
see whether you really want to take a hash value for granted. If a
property of the python language fails the bet the lives of your nearest
and dearest on a consistent result test, I call it ill defined and,
subjectively speaking, I prefer exceptions to be thrown--And, by damned,
I'll throw them myself if I have to.
If it saves one life, it's worth it all.
James
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Re: hashability
Steven D'Aprano wrote: Well there you go -- why on earth would you prohibit None as a dictionary key??? That's a serious failure. roentgen 1% python Python 2.5 (r25:51908, Sep 20 2006, 17:36:21) [GCC 3.4.2] on linux2 Type help, copyright, credits or license for more information. py hash(None) 135543872 mbi136-176 98% /usr/bin/python Python 2.5.1 (r251:54863, Feb 6 2009, 19:02:12) [GCC 4.0.1 (Apple Inc. build 5465)] on darwin Type help, copyright, credits or license for more information. py hash(None) 2030240 That's why. Read the whole thread. You are one of the abrasive ones. -- http://mail.python.org/mailman/listinfo/python-list
hashability
Hello All,
I wrote the function to test hashability of arbitrary objects. My reason
is that the built-in python (2.5) hashing is too permissive for some
uses. A symptom of this permissiveness comes from the ability to
successfully hash() arbitrary objects:
py class C(object): pass
...
py {C():4}[C()]
Traceback (most recent call last):
File ipython console, line 1, in module
type 'exceptions.KeyError': __main__.C object at 0xe21610
The basis for the exception is that the two instances do not have the
same hash() although conceptually they might seem equal to the
unitiated. Were I to re-design python, I'd throw an exception in this
case because of the ill-defined behavior one might expect if a C()
serves as a key for a dict.
To prevent users of one of my libraries from falling into this and
similar traps (which have potentially problematic consequences), I came
up with this test for hashability:
def hashable(k):
try:
hash(k)
except TypeError:
good = False
else:
good = (hasattr(k, '__hash__') and
(hasattr(k, '__eq__') or hasattr(k, '__cmp__')))
return good
It works as I would like for most of the cases I can invent:
py all(map(hashable, [1,1.0,,(1,2,3)]))
True
py any(map(hashable, [None, [1,2], {}, C(), __import__('sys')]))
False
Can anyone think of boundary cases I might be missing with this approach?
James
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Re: hashability
Carl Banks wrote:
On Aug 11, 5:54 pm, James Stroud jstr...@mbi.ucla.edu wrote:
To prevent users of one of my libraries from falling into this and
similar traps (which have potentially problematic consequences),
Even so, I would consider whether some of your users might, like me,
also find this terribly useful, and if so (probably a few will unless
they are all novices), allow them to disable or disregard this check.
I realize I left out my use. The intent of the function is to flag
objects that will make useful keys for a persistent dictionary. The
{C():4}[C()] example demonstrates why I want to avoid certain types of
keys--I don't want users to do things like {C():4, C():4}, which python
happily allows but falls apart at the level of persistence.
However, I also want to avoid isinstance() and/or type checking in order
to allow maximal flexibility so that users don't have to work too hard
to make their keys.
I wouldn't call the function hashable. Class instances like C() are
hashable whether you approve or not. Something like
deliberately_hashable would be a better name.
I chose keyable.
Can anyone think of boundary cases I might be missing with this approach?
It is possible to redefine == operator by defining __ne__ instead of
__eq__, at least on Python 2.5, so you should keep that in mind.
Thanks for this hint. I've already put it in.
James
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Re: hashability
Asun Friere wrote:
On Aug 12, 12:15 pm, James Stroud jstr...@mbi.ucla.edu wrote:
I realize I left out my use. The intent of the function is to flag
objects that will make useful keys for a persistent dictionary. The
{C():4}[C()] example demonstrates why I want to avoid certain types of
keys--I don't want users to do things like {C():4, C():4}, which python
happily allows but falls apart at the level of persistence.
What am I missing here? How, in terms of persistence, is {C():4, C():
4} conceptually different from {'spam':4, 'ham':4}?
You should be more imaginative.
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Re: hashability
Asun Friere wrote: Perhaps the best solution would be for the unitiated to correct their misaprehensions Can you come give a class to my users? -- http://mail.python.org/mailman/listinfo/python-list
Re: Frustrated with scopes
andrew cooke wrote: Is there a way to make this work (currently scope and join are undefined at runtime when the inner class attributes are defined): class _StreamFactory(object): @staticmethod def __call__(lines, source, join=''.join): class Line(object): __source = source __join = join [...] It would be helpful if you were to describe the type of behavior you expect. I assume you will return the newly created Line class when you call an instance of _StreamFactory? There may be some things about the above that you might be overlooking: 1. __call__ does not supersede the __init__ constructor of _StreamFactory. 2. __source and __join are name-mangled in later versions of python. They will be attributes of the returned Line class named _Line_source and _Line_join respectively. Rather than make _StreamFactory a class, you will probably get the behavior you desire if you simply make it a function: def stream_factory: class Line(object): __source = source __join = join # etc. return Line And then don't forget that double underscores produce name mangling and you'll be set. James -- http://mail.python.org/mailman/listinfo/python-list
Python quirk in evaluation order
Python 2.5: mbi136-176 211% python *** Pasting of code with or ... has been enabled. ## ipython ## py b = 4 if True else b py b 4 Isn't the right side supposed to be evaluated first? -- http://mail.python.org/mailman/listinfo/python-list
Re: TkInter: Problem with propagation of resize events through geometry manager hierarchy?
Randy Smith wrote: The cropping and scrolling works fine. But when I try to add responding to resize events, I get into trouble. Specifically: * When I naively change the size of the image shown to be borderwidth less than the size indicated in the configure event, the size of the image shown grows gradually but inexorably when I start the test app. (Sorta scary, actually :-}) * When I fiddle a bit to figure out what the actual difference in size is between the Configure event and the image that can be displayed, I get a vibrating, jagged display of the image. Investigation suggests that multiple configure events are hitting the label in response to each user resize with different sizes. I'm guessing that when I resize the image in response to those different events, that creates new resize events propagating through the window manager hierarchy, which creates new configure events, which means my handler changes the image size, which ... you get the idea. I can't test your code because I don't have the test image and for some reason it does not recognize a tiff of my own. But, just glancing at your code, it looks like a quick-fix would be to set self.zoom to a sentinel at the end of refresh() and return 'break' at the top of the methods that use self.zoom if it is said sentinel value (e.g. if self.zoom == WHATEVER_SENTINEL: return 'break'). You may also want to return 'break' for event responders that should terminate the event chain. This is a general technique to stop a lot of unwanted event propagation. James -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
Re: TkInter: Problem with propagation of resize events through geometry manager hierarchy?
curiouserra...@gmail.com wrote: Thanks! I hadn't known about the return 'break' technique. But I don't follow your sentinel suggestion; how would that sentinel ever get reset? Presumably you would set it from some kind of input. Basically, if you don't need to zoom, you wouldn't bother scaling the image. It is the scaling step that is expanding your image. You might want to set any borders to 0. It seems as if the first time through the event chain it'd be set to the sentinel, and the routines that pay attention to it would never execute. What am I missing? I tried simply returning 'break' at the end of refresh() and that made no change in behavior. You will want to return 'break' at the end of callbacks, like display_tag_and_size() One thing I've been looking for (including in the source :-J) is a description of the precise process that the geometry manager goes through in figuring out and then setting sizes for the various widgets (on resize or, apparently, startup). I suspect with that + the return 'break' technique I could get this to work. But I haven't been having any luck finding that documentation. I've never found that either. I usually tweak things by trial and error. Tkinter (Tk) has some bad habits. Most of the time it is very hard to get the precise dimensions of widgets by asking them. The problem is exacerbated by platform specific modifications like TkAqua. Ive found the best approach is to tweak the math so that the sizing comes out consistent and then test and patch for every platform you support. Sometimes, if you experiment enough, you can figure out by inference what Tk is actually doing under the hood. The other, more sane option, is to attempt to make guis that don't rely on precise size information. Its less satisfying than the pixel level control one hopes for, but makes for a faster development process. Also, you might want to look into Pmw. It has scrolled canvas and scrolled frame widgets that might be helpful to you. There is no need to reinvent the wheel except for your own enlightenment. James -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Is c.l.py becoming less friendly?
Tim Chase wrote: Is this where we tell you to shut up? gdr ;-) Don't you mean STFU? -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
Re: what IDE is the best to write python?
mcheun...@hotmail.com wrote: Hi all what IDE is the best to write python? thanks from Peter (mcheun...@hotmail.com) vim in one terminal, ipython in the other. -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
Re: dicts,instances,containers, slotted instances, et cetera.
ocsch...@gmail.com wrote: I can't port the entire app to be a stored database procedure. Perhaps I underestimate what you mean by this, but you may want to look at pyTables (http://www.pytables.org/moin/HowToUse). ctypes, maybe. I just find it odd that there's no quick answer on the fastest way in Python to implement a mapping in this context. Your explanation of where your prototype is slow is a little unclear. If your data is largely numerical, you may want to rethink your organization and use a numeric package. I did something similar and saw an order of magnitude speed increase by switching from python data types to numpy combined with careful tuning of how I managed the data. You may have to spend more time on this than you would like, but if you really put some thought into it and grind at your organization, you can probably get a significant performance increase. James -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
Re: New to python, open source Mac OS X IDE?
joseph.a.mar...@gmail.com wrote: Greetings! I've heard enough raving about Python, I'm going to see for myself what all the praise is for! I'm on a Mac. I use Netbeans for Java, PHP, and C if needed. Do you even use an IDE for Python? Any recommendations on open source Python environments? Thanks! Try open komodo. I haven't used it because vim is my IDE, but it looks pretty good. James -- http://mail.python.org/mailman/listinfo/python-list
Re: Start Python at client side from web app
Thomas Guettler wrote: Hi, I want to start Python at the client side from a web application. The app is an intranet application, and all client PCs are under our control (we can install software on them). But I don't want to update the installation too often. Here is my idea: We create a custom mime-type and register it on the client PC. The web application can send signed python code to the client PC. If the signature is correct, the code will be executed at the client. The signature prevents others from executing code. Has someone seen or done something like this before? I can code this myself, but prefer to use some open source project, if it exists. Thanks in advance, Thomas Güttler You are better off using a cron job (or similar) on the client side, getting the client to hit the web server for the code at regular intervals, and if code is ready, execute. If code isn't ready, wait for the next interval. Use https for security and have a shared secret message to identify legitimate clients. If you try to push code the other way, you will need a perpetual socket open on the client side, making the client the server. James -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Start Python at client side from web app
Thomas Guettler wrote: Sorry, I described my problem not well. Here is more information: The main application is the intranet web application used with IE (ms windows client). But some action needs to be done on the client since you can't do it with html or javascript. 1. The user pushes a button in the web app. 2. Webserver sends signed python code to the client with own mime type 3. IE sends code to the python application. 4. Signature gets checked, Python code on the client gets executed. 5. Maybe send some data to the server with http. You need to write an IE plugin for this, otherwise you can't get out of the browser sandbox to execute anything on the client side. In fact, if you just make your IE application a plugin, you can take advantage of updating facilities that IE should have for plugins. If IE doesn't have updating facilities, then just write a firefox plugin, which does have these facilities. -- http://mail.python.org/mailman/listinfo/python-list
Re: defining class functions
Astan Chee wrote: Hi, I have two classes in python that are in two different files/python scripts. Class A uses Class B like this: class B(object): def function1(self,something): pass def function2(self,something): print hello one print something class A(object): def __init__(self): instance = B() instance.function2(hello two) self.function3() def function3(self): print hello three What I want to do here is to (re)define function1 from function3. Is that possible? Is there any way of redefining a function of another class without inheriting it? Does this make sense? I know what you mean, but it doesn't make a lot of sense. Best practice is to make the function module level, especially if self is not referenced beyond the function definition. If self is referenced, then all selves must share the same behavior if not the same heredity, and using a module level function is still best: def function(quacker): print hello there quacker.quack() James -- http://mail.python.org/mailman/listinfo/python-list
Re: dynamic module import?
Lawson Hanson wrote:
So is there any way to get Python to import the named module
without just doing from dummy import *, because I will
not know that the user wants to use the dummy module
until run-time ... I'm trying to import control data
for different run scenarios which will be defined in
differently named Python modules which the user will
specify at run-time with a command-line option
And help with this would be most appreciated
For the sake of humanity, I must try to talk you out of this. Well, it's
not that serious, but dynamic import confuses programs that inspect code
like py2exe, etc. I think it is likely that you will find the day that
you regret trying so hard to 'import *' dynamically. A more maintainable
way is to simply map the command line argument to an import statement
and keep your namespaces clean:
importer_module
import sys
import dummy
import bonafide
modules = {dummy : dummy, bonafide : bonafide}
module = modules[sys.argv[1]]
If you have several modules that themselves might need the conditional
imports, simply put the import statements in a separate module (e.g.
importer_module and do something like
another_module
from importer_module import module
If you simply don't want to import a bunch of modules, use an if/then
statement. In any event, I advise you to not design your code or usage
around dynamic imports using the __import__() statement or exec().
James
--
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UCLA-DOE Institute for Genomics and Proteomics
Box 951570
Los Angeles, CA 90095
http://www.jamesstroud.com
--
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Re: Pythonic way to handle coordinates
Pierre-Alain Dorange wrote:
What is the elegant way to handle coordinates ?
Do i need to continue using tuples or do i need to write a Point class.
I feel a point class would be nice, because i could implement operators
with it ? But i think Point class must exist allready ?
My instinctive advice is to use a point class. My wise advice is to put
it in a library you will maintain and reuse--or else you will find
yourself re-writing point classes all of the time.
A Point class will also give you a place to consolidate all of those
methods specific to manipulating points. Thanks to python magic methods,
you can also design some nifty shortcuts to access the attributes of
your point.
Here is a fun example for no other reason than I'm too tired to do
anything important right now:
class Point(object):
def __init__(self, axes):
self.axes_names = axes.split()
self.axes = dict(enumerate(self.axes_names))
for axis in self.axes_names:
setattr(self, axis, 0.0)
def check_axis(self, i):
if i not in self.axes:
raise ValueError, No such axis %s % i
def __setitem__(self, i, v):
self.check_axis(i)
setattr(self, self.axes[i], v)
def __getitem__(self, i):
self.check_axis(i)
return getattr(self, self.axes[i])
def __iter__(self):
return (getattr(self, i) for i in self.axes_names)
def move(self, other):
for i, v in enumerate(other):
self[i] += v
def magnitude(self):
import math
return math.sqrt(sum(v**2 for v in self))
E.g.:
py p = Point('x y z')
py list(p)
[0.0, 0.0, 0.0]
py p.move([2, 3, 4])
py p.x, p.y, p.z
(2, 3, 4)
py p[0], p[1], p[2]
(2, 3, 4)
py list(p)
[2, 3, 4]
py tuple(p)
(2, 3, 4)
py p.magnitude()
5.3851648071345037
py q = Point('x y z')
py q.move([1, 2, 3])
py p.move(q)
py list(p)
[3.0, 5.0, 7.0]
py p[1] = 15.0
py list(p)
[3.0, 15.0, 7.0]
With the introduction of the second point, q, one can begin to see the
necessity for a class factory that produces Point classes of the desired
dimensionalities in desired coordinate systems:
def point(axes):
class P(Point):
def __init__(self, values):
Point.__init__(self, axes)
self.move(values)
return P
Note that we have have not used metaclasses--which would require messier
code but produce classes that would potentially behave a better as super
classes.
The point function is used as simply as it is written:
py Point3D = point('x y z')
py p = Point3D([0.0, 0.0, 0.0])
py list(p)
[0.0, 0.0, 0.0]
py q = Point3D([5.0, 6.0, 7.0])
py list(q)
[5.0, 6.0, 7.0]
py p.move(q)
py list(p)
[5.0, 6.0, 7.0]
Incidentally, the classes returned by point are heritable, etc.
class Point3D(point('x y z')):
def __repr__(self):
return Point3D(%s) % list(self)
def __add__(self, other):
return Point3D(sum(t) for t in zip(self, other))
py p = Point3D([8, 7, 6])
py p
Point3D([8.0, 7.0, 6.0])
py str(p)
'Point3D([8.0, 7.0, 6.0])'
py q = Point3D([5, 4, 3])
py r = p + q
py r
Point3D([13.0, 11.0, 9.0])
Now have fun with this stuff. I need to go to sleep.
James
--
James Stroud
UCLA-DOE Institute for Genomics and Proteomics
Box 951570
Los Angeles, CA 90095
http://www.jamesstroud.com
--
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Re: lazy evaluation is sometimes too lazy... help please.
Ken Pu wrote: Hi, below is the code I thought should create two generates, it[0] = 0,1,2,3,4,5, and it[1] = 0,10,20,30,..., but they turn out to be the same!!! from itertools import * itlist = [0,0] for i in range(2): itlist[i] = (x+(i*10) for x in count()) print what's in the bags: print list(islice(itlist[0], 5)) print list(islice(itlist[1], 5)) The output is: [10, 11, 12, 13, 14] [10, 11, 12, 13, 14] I see what Python is doing -- lazy evaluation doesn't evaluate (x+(i*10) for x in count()) until the end. It doesn't evaluate it until you ask it to, which is the right behavior. However, when evaluated, it evaluates i also, which is the last value to which i was assigned, namely the integer 1. I'm going to get flamed pretty hard for this, but it doesn't seem to be the intuitive behavior to me either. However, in a purely functional language, you wouldn't be able to construct a list of generators in this way. With python, you have to remember to adopt a purely functional design and then pray for best results. You can store generators in a list, but they need to be constructed properly. I can't perfectly transmogrify your code into functional code because I don't think making the particular anonymous generator you want is possible in python. However this is how I would make a close approximation: from itertools import * def make_gen(i): for x in count(): yield x + (i * 10) itlist = [make_gen(i) for i in xrange(2)] print what's in the bags: print list(islice(itlist[0], 5)) print list(islice(itlist[1], 5)) James -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
Re: General direction
MLT wrote: Hello all: I'm a beginner to Python (and programming altogether), and am now looking to create a program of my own. What I've got in mind is a very basic pest control program that would keep track of 1) trap findings and 2) pesticides. My thought is to make each of these classes. Looking at the general outline written below, can anyone give general impression about whether I'm somewhat going in the right direction or if I need to approach it entirely differently? Thanks for any suggestions or help! [data structures snipped] Programs generally *do* something. Here you have described data structures, which just sit there being full of data. They aren't very active and hence are not terribly interesting. Here are some bullet points for your consideration: 1. What will your program do? 2. Understand databases (http://tinyurl.com/6flhbz) before you start. 3. Consider PySQlite (http://trac.edgewall.org/wiki/PySqlite) before you think about a heavyweight database backend (once you realize that you will want a database for this project). James -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Suggested improvements for IDLE (non-official)
r wrote: I actually like the IDLE, but it could use a few improvements. If anybody else has suggestions by all means post them. 1.) The text widget and the prompt() should be separated. Trying to write a conditional in the interactive IDLE is a real PITA. Not to mention if you copy the working code snippet to the IDLE editor window the indention is 8 spaces instead 4 AND you've got that prompt() stuck in there. I have a solution for the problem though.( I hope you all are using fixed-width font) frm |-text widget - | |if this == 1: ... |if that == 2: ... |#do ... |elif that ==3: ... |#do ... |else: ... |pass | |x = 10 Brilliantly put. This is probably the main reason that IDLE is not worth using. Good luck on getting this changed. Best is to find yourself another IDE. Try vim. Basically you have a Listbox on the left for the prompt and a Text on the right. Disable the Listbox highlight and key press events and now we have a very friendly interactive IDLE! No more prompt hijacking your snippets, and no more 8 space indention! Excellent suggestions are a dime a dozen. Finding people to implement them is slightly harder. Getting said suggestions accepted into the python distribution is nearly impossible. Accept what you are given and try vim. If you really want a cool IDE, try Leo. It had some bugs about 4 years ago when I tried it, but I'm sure they have been worked out now. I'm addicted to vim, but if I wasn't, I'd probably be using Leo. James -- http://mail.python.org/mailman/listinfo/python-list
Re: hlep: a text search and rename question
sensen wrote:
matter description:
when a use an tools to do the ape to flac convert, i can use the cue
file attached with ape, but the problem is the converted flac file
don't name by the title in the cue file but like Track_1.flac,
Track_2.flac ... , so i want to write a script to do this work, system
is xp sp2, the python is 2.44, i have a plone site in this computer,
that is why i want to use python to do this work.
so simplify and example
CDImage.cue, Track_1.flac, Track_2.flac, Track_3.flac, Track_4.flac
all above files in the same folder.
the cue file is just a text file like bellow:
PERFORMER Dido
TITLE Life For Rent
FILE Dido - Life for Rent.ape WAVE
TRACK 01 AUDIO
TITLE White Flag
PERFORMER Dido
INDEX 01 00:00:00
TRACK 02 AUDIO
TITLE Stoned
PERFORMER Dido
INDEX 00 04:00:03
INDEX 01 04:01:45
TRACK 03 AUDIO
TITLE Life For Rent
PERFORMER Dido
INDEX 00 09:56:47
INDEX 01 09:56:53
TRACK 04 AUDIO
TITLE Mary's In India
PERFORMER Dido
INDEX 01 13:37:57
the things i want to do
1. search the current folder cue file (only one cue file) contents.
find the TITLE White Flag and get the White Flag and maybe we
can save it to a var.
2. then rename the Track_1.flac to the White Flag.flac
3. search the next title TITLE Stoned and save ti to var.
4. then rename the Track_2.flac to the Stoned.flac.
5. do the same things to the end title.
someone can give some outline, or code is more wonderful. thanks in
advance.
This isn't much work in python:
import os, glob, re
cue = iter(open('CDImage.cue').readlines())
titles = []
for line in cue:
if line.strip().startswith('FILE'):
break
for line in cue:
if line.strip().startswith('TITLE'):
titles.append(line.split('')[-2])
flacs = glob.glob('*.flac')
flacs.sort(key=lambda f: int(re.search(r'\d+', f).group(0)))
for old, new in zip(flacs, titles):
os.rename(old, new)
There is no error checking for properly formatted cue file, etc.
James
--
James Stroud
UCLA-DOE Institute for Genomics and Proteomics
Box 951570
Los Angeles, CA 90095
http://www.jamesstroud.com
--
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Re: hlep: a text search and rename question
James Stroud wrote:
cue = iter(open('CDImage.cue').readlines())
It just occurred to me that this could simply be:
cue = open('CDImage.cue')
James
--
James Stroud
UCLA-DOE Institute for Genomics and Proteomics
Box 951570
Los Angeles, CA 90095
http://www.jamesstroud.com
--
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Re: Unbinding Tkinter default bindings for Listbox
Roger wrote:
Hi Everyone,
I have a behavior associated with a default binding with Tkinter
Listbox that I want to get rid of but I can't no matter if I return
break on the binding or unbind it directly. If you have a Listbox
where the bounding box is not completely revealed in the window that
holds it and you use the mouse to drag the list box, the contents of
the listbox will move in the X direction to reveal the area that's
hidden. After searching the internet for hours I found the behavior I
want to remove is a default binding as described here:
http://tcltk.free.fr/man/TkCmd/listbox.php3
[3] If the mouse leaves the listbox window with button 1 down, the
window scrolls away from the mouse, making information visible that
used to be off-screen on the side of the mouse. The scrolling
continues until the mouse re-enters the window, the button is
released, or the end of the listbox is reached.
After further searching I found that the code for this in tcl is
described here:
http://www.openmash.org/lxr/source/library/listbox.tcl?c=tk8.3
50 bind Listbox B1-Motion {
51 set tkPriv(x) %x
52 set tkPriv(y) %y
53 tkListboxMotion %W [%W index @%x,%y]
54 }
Now I've found no way to successfully unbind B1-Motion from the
listbox, as I said above. Nor return break on receiving the event.
I do want to eventually have my own B1-Motion binding applied to the
listbox for a different reason (with add='+' if necessary). My next
step was to see if I could just unbind B1-Motion then programmatically
delete tkListboxMotion in my code but tkListboxMotion is not available
in the Tkinter source (it's part of a compiled binary I can't reach?).
Any help would be greatly appreciated. Thanks!
Roger.
You can directly send commands to the Tcl interpreter via the call
method of the tk attribute of any Tkinter widget. For example:
py from Tkinter import *
py tk = Tk()
py b = Button(tk)
py b.pack()
py b.tk
tkapp object at 0xd57720
py b.tk.call('bind', 'Listbox', 'B1-Motion')
'\nset tk::Priv(x) %x\nset tk::Priv(y) %y\ntk::ListboxMotion
%W [%W index @%x,%y]\n'
py b.tk.call('bind', 'Listbox', 'B1-Motion', _)
''
James
--
James Stroud
UCLA-DOE Institute for Genomics and Proteomics
Box 951570
Los Angeles, CA 90095
http://www.jamesstroud.com
--
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Re: Unbinding Tkinter default bindings for Listbox
James Stroud wrote:
py b.tk.call('bind', 'Listbox', 'B1-Motion', _)
You want b.tk.call('bind', 'Listbox', 'B1-Motion', ) of course.
James
--
James Stroud
UCLA-DOE Institute for Genomics and Proteomics
Box 951570
Los Angeles, CA 90095
http://www.jamesstroud.com
--
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Re: Unbinding Tkinter default bindings for Listbox
Roger wrote:
I'm sorry for harassing the list but any suggestions would be greatly
appreciated. =)
I just checked the behavior you are describing. It seems that you want
to unbind the Leave event to stop the autoscrolling when you leave the
listbox. E.g.:
from Tkinter import *
tk = Tk()
lb = Listbox(tk)
lb.pack()
tk.tk.call('bind', str(lb), 'Leave', break)
for i in range(12):
lb.insert(END, str(i))
Sorry for not reading more carefully.
James
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Re: Unbinding Tkinter default bindings for Listbox
James Stroud wrote:
tk.tk.call('bind', str(lb), 'Leave', break)
Which is equivalent to
lb.bind('Leave', break)
But I checked and overriding the default behavior of Listbox does not
work (tk.tk.call('bind', Listbox, 'Leave', break)).
So I would subclass Listbox and do the bindings in the __init__:
class MyListbox(Listbox):
def __init__(self, *args, **kwargs):
Listbox.__init__(self, *args, **kwargs)
self.bind('Leave', break)
James
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Re: Unexpected behavior with dictionary keys containment and a user-defined class
Rob Clewley wrote: Hi, the short version of my question is: when is a dictionary's __contains__ method behavior different to using the 'in' idiom? (because I have an example of a difference in my code). Never. Longer version: I have a user-defined class with a few overrides of special methods, particularly __eq__ and __ne__. I also have a dictionary keyed by instances of these classes, and I'm confused about the unexpected behavior trying to test whether an instance is in the dictionary's keys. The instance is i and the dictionary is d. I have been using the idiom i in d which I understood to be the pythonic way to test the keys, but it doesn't work. However, when I debug my code I see the instance in the list of keys, and in fact i in d.keys() and d.keys()[10] == i both return True. But d.__contains__(i) d.has_key(i) d.keys()[10] is i return False. I put a print statement in my class's __eq__ method and it is being called. It tests equality of some of my class instance's attributes. I didn't realize there was any situation where you could expect different results from i in d versus i in d.keys() -- am I misunderstanding something? Well, the only conclusion is that dict uses the hash of an object to test containment while lists use id. James -- http://mail.python.org/mailman/listinfo/python-list
Re: drive a desktop app from python?
Tim Arnold wrote:
Hi, I don't even know what to google for on this one. I need to drive a
commercial desktop app (on windows xp) since the app doesn't have a batch
interface. It's intended to analyze one file at a time and display a
report.
I can get the thing to write out the report an html browser, but I have
thousands of files I need it to analyze every night.
Is there any lib or recipe(s) for doing something like this via python?
You are a little thin on details here. My only advice at this point is
to check out os.system, which is the simplest option. From there you can
move to the popen2 module for greater control, but if you are talking
about a gui app, you may run into hang-ups.
A quick recipe would be the following pretend application that
recursively descends from the current directory calling the utility
named dosapp on every file it finds that ends with jpg (what
dosapp does is left to your imagination):
import os
def doit(suffix, adir, filenames):
for afile in filenames:
if afile.endswith(suffix):
pathname = os.path.join(adir, afile)
os.system('dosapp %s' % pathname)
top = '.'
suffix = '.jpg'
os.path.walk(top, doit, suffix)
Read the docs on os.path.walk, of course.
James
--
James Stroud
UCLA-DOE Institute for Genomics and Proteomics
Box 951570
Los Angeles, CA 90095
http://www.jamesstroud.com
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Re: Oh! The people of all over the world!
Obaid R. wrote: So an illegal occupation is NOT a provocation but fighting the occupation IS? By which scales do you judge? I would argue that a person following such backwards logic and who sees these pictures[1] and STILL claims that showing sympathy is difficult has a serious problem. After all the logic is simple: for every action (read occupation) there is a reaction (read resistance) equal to it in force and opposite to it in direction. You can of course argue that the reaction is the cause of the action, but that is clearly illogical and proves your iniquity in this matter and your bias against the victim. It might take a humanitarian catastrophe of sizable proportions and a biased person would still not feel any sympathy. Not that there is no catastrophe, but rather because bias is by nature practiced in spite of good reason and available evidence, not because of it. I'm much more apt to listen now that you aren't invoking references to religion at every sentence. If Israel is guilty of inhumanity, then it is more appropriate to appeal to one's humanity. By the way, its obvious to most rational people that the Israeli reaction is overwrought and likely morally unjust--but I can't stand antisemitism just like I can't stand hatred of Islam just like I can't stand hatred of Christians. James -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
Re: How to store passwords?
Oltmans wrote: I'm writing a program in which I will ask users to enter user name and password once only. It's a console based program that will run on Windows XP. Actually, I'm trying to provide the similar functionality as Remember me thing in browsers. For that, I will need to store user name and passwords on the disk. I don't have a background in Crypto so how do you suggest I do that? What algorithms shall I be using? Moreover, I cannot use a whole library to do that due to certain issues. However, I can use like 1--2 files that will be shipped along with the main script. Any ideas? Any help will be really appreciated. Thanks. There is a pure python implementation of blowfish out there. Google will help you. I can't remember which, if any, types of block chaining it supports. In some cases, it is important to use a block chaining protocol, but for passwords with high entropy (ie good passwords), block chaining is not really necessary. 256 bit Blowfish or AES are adequate for storage of sensitive passwords. You would be well advised to read a manual like Schneier before you use cryptography for sensitive applications. Pitfalls exist even when you use a strong algorithm and think you know what you are doing. Stay away from stream ciphers. They are easy to screw up. Don't attempt to use DES, etc., for this either, they are not secure enough. Don't pretend that you can invent your own cipher either just in case the thought might cross your mind. Google adacrypt for some hilarity in this area. If you check out sf.passerby.net and download the source, you will see a pure python module in there called jenncrypt which can help with buffering and has minimal fileIO type emulation for block ciphers, which you will appreciate when you try to use your block cipher for plaintexts of irregular sizes. James -- http://mail.python.org/mailman/listinfo/python-list
Re: How to store passwords?
James Stroud wrote: Oltmans wrote: I'm writing a program in which I will ask users to enter user name and password once only. It's a console based program that will run on Windows XP. Actually, I'm trying to provide the similar functionality as Remember me thing in browsers. For that, I will need to store user name and passwords on the disk. I don't have a background in Crypto so how do you suggest I do that? What algorithms shall I be using? Moreover, I cannot use a whole library to do that due to certain issues. However, I can use like 1--2 files that will be shipped along with the main script. Any ideas? Any help will be really appreciated. Thanks. There is a pure python implementation of blowfish out there. Google will help you. I can't remember which, if any, types of block chaining it supports. In some cases, it is important to use a block chaining protocol, but for passwords with high entropy (ie good passwords), block chaining is not really necessary. 256 bit Blowfish or AES are adequate for storage of sensitive passwords. You would be well advised to read a manual like Schneier before you use cryptography for sensitive applications. Pitfalls exist even when you use a strong algorithm and think you know what you are doing. Stay away from stream ciphers. They are easy to screw up. Don't attempt to use DES, etc., for this either, they are not secure enough. Don't pretend that you can invent your own cipher either just in case the thought might cross your mind. Google adacrypt for some hilarity in this area. If you check out sf.passerby.net and download the source, you will see a pure python module in there called jenncrypt which can help with buffering and has minimal fileIO type emulation for block ciphers, which you will appreciate when you try to use your block cipher for plaintexts of irregular sizes. James Before anyone jumps me, I just realized the point is authentication. Use a hash as others have suggested. James -- http://mail.python.org/mailman/listinfo/python-list
Re: How to store passwords?
James Stroud wrote: If you check out sf.passerby.net and download the source, you will see a passerby.sf.net Shuffle things I did. -- http://mail.python.org/mailman/listinfo/python-list
Re: Regular Expressions...
Ken D'Ambrosio wrote: Hi, all. As a recovering Perl guy, [snip] In Perl, I'd so something like m/^1(...)(...)/; Indeed it seems you are recovering from an especially bad case. I recommend two doses of the python cookbook per day for one to two months. Report back here after your first cycle and we'll tell you how you are doing. I'm very optimistic about the prognosis. James -- http://mail.python.org/mailman/listinfo/python-list
Re: Is it ok to type check a boolean argument?
Adal Chiriliuc wrote: Hello, Me and my colleagues are having an discussion about the best way to code a function (more Pythonic). Here is the offending function: def find(field, order): if not isinstance(order, bool): raise ValueError(order must be a bool) order_by = asc if order else desc return _find(field + + + order_by) We are not sure what's the best practice here. Should we or should we not check the type of the order variable, which should be a bool? None of the above. You have put unnecessary constraints on find by requiring a certain data type. def find(field, order_by='desc'): return _find(field + + + order_by) Here we are deferring error checking to the _find function. Otherwise: def find(field, order_by='desc'): if order_by not in ['asc', 'desc']: raise ValueError, 'Bad order_by parameter.' else: return _find(field + + + order_by) Now you have achieved the exact same affect without any sort of explicit type checking. Moreover, you have eliminated an if statement. Also, you leave room for exotic orderings should you ever want them. James -- http://mail.python.org/mailman/listinfo/python-list
Re: Is it ok to type check a boolean argument?
Ben Finney wrote: Why are people so reluctant to make error message templates clearer with named placeholders? Because they can never remember they even exist. Thanks for the reminder. -- http://mail.python.org/mailman/listinfo/python-list
Re: Generator metadata/attributes
acooke@gmail.com wrote: Hi, (I searched back and found some previous discussion on generator attributes that seemed to be related to callable generators - this is NOT that, as far as I can tell) I want to associate some data with a generator. This is in a decorator function, as it happens; the generator is being returned and I want to add some info that is useful for debugging later. I have tried modifying both .__doc__ and an arbitrary attribute, but the first is read-only, and the second does not exist (ie you cant just add one by writing to it; same error with setattr). I realise I could create my own wrapper that implements __next__ That is what you are going to have to do. Immutable python builtins work that way: py i = 4 py i.bob = 2 Traceback (most recent call last): File ipython console, line 1, in module type 'exceptions.AttributeError': 'int' object has no attribute 'bob' py i.__doc__ = 'I am an int' Traceback (most recent call last): File ipython console, line 1, in module type 'exceptions.AttributeError': 'int' object attribute '__doc__' is read-only James -- http://mail.python.org/mailman/listinfo/python-list
Re: What would you like to see in a book about Matplotlib?
Sandro Tosi wrote: Hello and Happy 2009! I received the interesting proposal to author a book on Matplotlib, the powerful 2D plotting library for Python. While preparing the arguments list, I'd like to hear even your opinion, because different points-of-view will lead to a better product. Some basic question I'd like to ask are: - what are you using matplotlib for? Matplot lib shines for interactive environments wherein graphs and charts must be produced. I have incorporated it into a simple program for analysis of fluorometric data: http://fluorit.bravais.net/ (The forthcoming version 1.0 is a quantum improvement in speed and function over the SLOW *prototype* version 0.9 currently available--see the wish list, feature requests, and known issues for details. Version 1.0 is very fast.) - what are the things you like the most of matplotlib, that you want to give emphasis to? And why? The ability to embed a figure (composed of subplots) into a custom window is my favorite aspect. Also: massive configurability of plots, event driven plot canvas, antigrain geometry antialiasing are also all very important. Additionally the toolbar of standard interactive functions and the ability to export plots in a variety of formats are also invaluable features. - what are the (basic) things that, when you were beginning to use matplotlib, you wanted to see grouped up but couldn't find? The documentation for basic plot configuration, especially for embedded plots, and also tapping into the event model is very weak currently. These need the most improvement. - what would you like to see in a book about matplotlib? A big, huge, gigantic, chapter---no make that 3 chapters--on programming interactivity with the plot canvas. - what are some those advanced feature that made you yell WOW!! ? I listed them above, but my most WOW moment was when I saw the Tkinter backend doing beautiful antialiasing. I was also very happy to seamlessly add new functionality to the toolbar. - what are the things you'd like to explore of matplotlib and never had time to do? I want to program a lot of interactivity with the plots in my current application. Your suggestions are really appreciated :) And wish me good luck! Good luck! I can't wait to read your book! James -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
Re: __builtin__ quote
Steven Woody wrote: Hi, I am a new leaner and I get a question: abs() is a member of __builtin__ module, but why should I use abs() rather than __builtin__.abs() ? Thanks. It saves typing. This might help your understanding: py import __builtin__ py __builtin__.abs is abs True James -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
Re: __builtin__ quote
Steven Woody wrote: On Tue, Jan 6, 2009 at 4:42 PM, James Stroud jstr...@mbi.ucla.edu wrote: py import __builtin__ py __builtin__.abs is abs True Does that mean someone did 'import * from __builtin__' when python startup? In terms of the exact implementation of the cPython interpreter, I don't know. But the interpreter behaves as if someone did just that. So there is nothing wrong with thinking of it this way if it helps you understand the interpreter. -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
Re: subclassing 'list'
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.
Any suggestions will be highly appreciated.
Best regards,
Aki-
Slice assignment will behave as you like:
py class Mylist(list):
... def arrange(self):
... new_value = [1, 2, 3]
... self[:] = new_value
...
py m = Mylist()
py m.arrange()
py m
[1, 2, 3]
Your other option is to arrange the list in-place, depending on what it
means to arrange the list. You may want to provide a more explicit example.
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Re: assignment with [:]
Ben Bush wrote: On Dec 26, 4:46 pm, Tim Chase python.l...@tim.thechases.com wrote: What does *not* work is 3 * [0,1,2] As you know, this gives [0,1,2,0,1,2,0,1,2] What I am hoping for is [0,3,6] I see that I can use numpy.multiply(3,range(3)) but this seems overkill to me. Can you tell I am coming to Python from Matlab? The common way to do this is just a1 = [0,1,2] a2 = [x * 3 for x in a1] or, if you need a1 to be done in place: a1[:] = [x*3 for x in a1] There is some subtlety here. The latter says to empty the list assigned to the name a1 and refill it with the products. Other references to the same list will now reflect this operation. This procedure is not equivalent to reassigning the name a1. For example: py a = [1, 2, 3] py a1 = a py a1[:] = [x*3 for x in a1] py a1 [3, 6, 9] py a1 [3, 6, 9] Whereas: py a = [1, 2, 3] py a1 = a py a1 [1, 2, 3] py a1 = [x*3 for x in a1] py a1 [3, 6, 9] py a [1, 2, 3] James -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
Re: assignment with [:]
James Stroud wrote: py a = [1, 2, 3] py a1 = a py a1[:] = [x*3 for x in a1] py a1 [3, 6, 9] py a1 [3, 6, 9] This should have been: py a = [1, 2, 3] py a1 = a py a1[:] = [x*3 for x in a1] py a [3, 6, 9] py a1 [3, 6, 9] James -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Is there a function to remove escape characters from a string ?
Stef Mientki wrote: hello, Is there a function to remove escape characters from a string ? (preferable all escape characters except \n). thanks, Stef import string WANTED = string.printable[:-5] + \n def descape(s, w=WANTED): return .join(c for c in s if c in w) James -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Multi-dimension list
Steven Woody wrote: Hi, In the book Python Essential Reference, Chapter 3, when talking about extended slicing, it gives an example: a = m[0:10, 3:20]. But I don't understand how the 'm' was defined. What should it looks like? m could be an instance of the Krayzee class. py class Krayzee(object): ... def __getitem__(self, i): ... try: ... r = ['WTF?' for j in i] ... except: ... r = 'WTF?' ... return r ... py m = Krayzee() py m[1:2:3, 4:5:6] ['WTF?', 'WTF?'] py m['your moms'] ['WTF?', 'WTF?', 'WTF?', 'WTF?', 'WTF?', 'WTF?', 'WTF?', 'WTF?', 'WTF?'] -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Strategy for determing difference between 2 very large dictionaries
Marc 'BlackJack' Rintsch wrote: On Wed, 24 Dec 2008 03:23:00 -0500, python wrote: Hi Gabriel, Thank you very much for your feedback! k1 = set(dict1.iterkeys()) I noticed you suggested .iterkeys() vs. .keys(). Is there any advantage to using an iterator vs. a list as the basis for creating a set? I understand that an iterator makes sense if you're working with a large set of items one at a time, but if you're creating a non-filtered collection, I don't see the advantage of using an iterator or a list. I'm sure I'm missing a subtle point here :) `keys()` creates a list in memory, `iterkeys()` does not. With ``set(dict.keys())`` there is a point in time where the dictionary, the list, and the set co-exist in memory. With ``set(dict.iterkeys())`` only the set and the dictionary exist in memory. For the purpose of perpetuating the annoying pedantry that has made usenet great: http://docs.python.org/dev/3.0/whatsnew/3.0.html#views-and-iterators-instead-of-lists James -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
Re: On Whose Desktop
Steve Holden wrote: Thanks to Barry Warsaw the On Your Desktop blog now has a new entry: Note the thumb trackball. It's the shiznizzle. Give one two weeks of your patience and you'll seriously consider having it implanted in your thigh so you don't have to worry about missing it when you travel. -- http://mail.python.org/mailman/listinfo/python-list
Re: alt.possessive.its.has.no.apostrophe
Ben Finney wrote: James Stroud jstr...@mbi.ucla.edu writes: Ben Finney wrote: James Stroud jstr...@mbi.ucla.edu writes: Yes. I think it was the British who decided that the apostrophe rule for it would be reversed from normal usage relative to just about every other noun. It also seems an indefensible claim to say that anyone “decided” it would be that way, especially “the British”. Remember that “it” is a pronoun. I see no reversal: Ok. Pronouns are reversed. Or, more generally: Pronouns, which are different in just about every other way from other nouns, are different in this way also. Is that about right? Can we start talking about python again? -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Need help improving number guessing game
feba wrote:
I don't see the aim of your changes to setup(). I can kinda understand
checking to make sure that you didn't make the minimum higher than the
maximum, but I think where you put minr/maxr would make it use the
same minr/maxr as the end of the previous game, wouldn't it?
No. Each function call creates its own name space. The function as Bruno
has written it will have default values (mini maxi). A call to this
function can set different values optionally:
setup(2) #== range from 2 to 99
setup(maxi=101) #== range from 1 to 101
setup(5, 10) #== range from 5 to 10
setup(10, 5) #== throws an error
Minor point for a short program, but still good practice : use
constants. IE :
I had done this initially, but it seemed wasteful and needlessly
confusing in this situation.
No. Tracking down and changing hard-coded values within a module is
wasteful and needlessly confusing. Creating well named and well
documented module level constants is good style and will make your life
easier in the long run.
I assume 'p1sc' means player_1_score ?
If so, you may want to use a dict for scores:
I don't really understand dicts yet; actually, the tutorial I'm
following (http://www.briggs.net.nz/log/writing/snake-wrangling-for-
kids/ , designed for tweens, but other than the pointless anecdote and
joke here and there, I've found it a very good guide) doesn't even
seem to mention them, from a search of the pdf. Actually, apparently I
stopped and started working on this just before the chapter on
functions and modules.
scores = {'player 1' : 0, 'player 2' : 0 }
scores['player 2'] = 10#== now player 2's score is 10
scores['player 1'] += 1#== now player 1's score is 1
print scores['player 0'] #== prints 0
print scores['player 2'] * 2 #== prints 20
If you get that, you'll have about all you need to know about dicts to
use them for keeping track of scores (and other values) in your game.
I'll look into that later on, but for now I'm pretty happy with how it
works.
Try it sooner rather than later. I didn't get this kind of advice when I
was first learning. It would have shaved months from my learning curve.
You should either put this in it's own function (could be named 'main'),
or at least protect it with an if __name__ == '__main__': test.
Could you go into a bit more detail on this? I don't understand what
should be its own function, nor do I understand what that line would
do or how to use it.
The idea is that everything you write is reusable and can be imported as
a module. Upon importing a module, it's code is executed. So, as
written, if someone imports it as a library module, they will start
playing the game. Wrapping in the if __name__ == '__main__': test
prevents the main loop of the game from executing on import. Only when
the module is __main__ will that test evaluate to true and its
commands execute.
For small programs like you have here, I'd do it like this (again
combining ideas):
def num_players(game, prompt='1 or 2 Players?\n '):
while True:
num = input(prompt)
try:
num = int(num)
except ValueError:
print Bad Value
else:
break
game['pnum'] = num
def main(game=None):
if game is None:
game = {}
print(WELCOME TO THE SUPER NUMBER GUESSING GAME!)
num_players(game)
game['play'] = 1
# P1 goes first
game['player'] = P1
#Scores, keep track of times player guessed first.
game['p1sc'], game['p2sc'] = 0, 0
setup(game)
while game['play'] == 1:
guessing(game)
if __name__ == __main__:
main()
I just threw a little advanced stuff at you. But you would be doing
yourself a huge favor if you struggled to understand it. The idea is
that since game is a dict, you can modify game inside of the functions,
and all you do is pass the game around to functions that need the values
of its contents.
For example:
def setup(game):
game['a'], game['b'] = 1, 99
game['target'] = random.randint(a, b)
def playagain(game):
playover = input(PLAY AGAIN? Y/N: )
if playover.strip().lower() == y:
game['play'] = 1
setup(game)
else:
print(GOOD BYE. PLAY AGAIN SOON!)
quit()
Notice that I just made return values obsolete.
You will also notice that management of all of your values now becomes
more tractable using the mutability of dict (game). Long, ugly lines
now become simple function calls. See if you can understand what I'm
doing here and try to propagate the idea through your game using the
game dict.
If you can do it, you'll be at least 80% of the way to understanding
object oriented programming, by the way.
James
--
James Stroud
UCLA-DOE Institute for Genomics and Proteomics
Box 951570
Los Angeles, CA 90095
http://www.jamesstroud.com
--
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Re: Optimizing methods away or not?
Steven D'Aprano wrote: class Parrot: def __init__(self, *args): print Initialising instance... if __debug__: self.verify() # check internal program state, not args if __debug__: def verify(self): print Verifying... +1 It looks good to me and the intent is much clearer than the other. -- http://mail.python.org/mailman/listinfo/python-list
Re: Need help improving number guessing game
It looks much better. But as Bruno suggests and as I alluded to earlier, you should get in the habit of forming verification loops on input channels that aren't already guaranteed to provide valid input messages. I'm not sure how to say that in English, but in python my example was: while True: try: guess1 = int(input(\n )) except ValueError: print 'Bad value.' else: break Other than that, you still have some points where you can break lines down to improve clarity. Think of it like trying to avoid run-on sentences. Over all, it looks like you have picked up some good technique that you could only get by experimentation over the course of about 5 or 6 months. James -- http://mail.python.org/mailman/listinfo/python-list
Re: Looking for the best way to translate an idiom
Paul Moore wrote:
I'm translating some code from another language (Lua) which has
multiple function return values. So, In Lua, it's possible to define a
function
function f()
return 1,2,3
end
which returns 3 values. These can then be used/assigned by the caller:
a,b,c = f()
So far, much like Python, but the key difference is that in Lua,
excess arguments are ignored - so you can do
py class mytuple(tuple):
def magic(self, astr):
names = astr.split()
for name, val in zip(names, self):
globals()[name] = val
...
py t = mytuple((1,2,3))
py t.magic('a b')
py a
1
py b
2
James
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Re: Looking for the best way to translate an idiom
James Stroud wrote:
py class mytuple(tuple):
def magic(self, astr):
names = astr.split()
for name, val in zip(names, self):
globals()[name] = val
...
py t = mytuple((1,2,3))
py t.magic('a b')
py a
1
py b
2
James
In case its not obvious:
def f():
return mytuple((1,2,3))
f().magic('a b')
You can parameterize lobbing off values, or use more magic:
py class mytuple(tuple):
... def magic(self, astr):
... names = astr.split()
... for name, val in zip(names, self):
... globals()[name] = val
... def __add__(self, other):
... if isinstance(other, tuple):
... return mytuple(tuple.__add__(self, other))
... else:
... return mytuple(self[other:])
...
py t = mytuple((1,2,3))
py t + 1
(2, 3)
py def f():
return mytuple((1,2,3))
...
py (f() + 1).magic('a b')
py a
2
py b
3
It's not as bad as a lot of the cynics are about to tell you it is. If
it has any badness at all, it's because of the need (according to what I
infer from your specification) to use the global namespace. If you want
to modify a more local namespace, you can use some stack frame
inspection to do some real magic:
py import inspect
py class mytuple(tuple):
def magic(self, astr):
names = astr.split()
for name, val in zip(names, self):
inspect.stack()[1][0].f_locals[name] = val
def __add__(self, other):
if isinstance(other, tuple):
return mytuple(tuple.__add__(self, other))
else:
return mytuple(self[other:])
...
py def f():
return mytuple((6,7,8))
...
py (f() + 1).magic('a b')
py a
7
py b
8
James
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Re: Looking for the best way to translate an idiom
drobi...@gmail.com wrote: I'm baffled by this discussion. What's wrong with a, dontcare, dontcare2 = f() a = a + 1 Simple, clear, and correct. 1. This can't apply to a generalized f() that may return an arbitrary number of arguments = len(num_assignments_you_care_about). 2. The example chosen was misleading. You don't want to add 1 to the first element of the tuple, you want to move the start of the returned tuple up 1 and start assignment on the left from there. James -- http://mail.python.org/mailman/listinfo/python-list
Re: Looking for the best way to translate an idiom
James Stroud wrote: inspect.stack()[1][0].f_locals[name] = val I just double checked this. Because of the way locals are implemented in cPython, this won't have the desired affect. James -- http://mail.python.org/mailman/listinfo/python-list
Re: Looking for the best way to translate an idiom
Aahz wrote: In article gi4834$la...@zinnia.noc.ucla.edu, James Stroud jstr...@mbi.ucla.edu wrote: In case its not obvious: Ah, so that's where Bruno's extra apostrophe came from! ;-) (Sorry about the spelling flame, but seeing three posts in quick succession with incorrect spelling of its/it's pushed me into making a public comment.) Yes. I think it was the British who decided that the apostrophe rule for it would be reversed from normal usage relative to just about every other noun. I'm not sure the purpose--maybe it was to give compulsive proofreaders a raison d'etre. -- http://mail.python.org/mailman/listinfo/python-list
Re: alt.possessive.its.has.no.apostrophe
Ben Finney wrote: James Stroud jstr...@mbi.ucla.edu writes: Yes. I think it was the British who decided that the apostrophe rule for it would be reversed from normal usage relative to just about every other noun. Remember that “it” is a pronoun. I see no reversal: Ok. Pronouns are reversed. Bob's Its -- http://mail.python.org/mailman/listinfo/python-list
Re: Looking for the best way to translate an idiom
I V wrote: On Sun, 14 Dec 2008 21:08:33 -0800, James Stroud wrote: Yes. I think it was the British who decided that the apostrophe rule for it would be reversed from normal usage relative to just about every other noun. I'm not sure the purpose--maybe it was to give compulsive proofreaders a raison d'etre. It's because it is a pronoun; you don't put an apostrophe in his, either. Its called humor. -- http://mail.python.org/mailman/listinfo/python-list
Re: Need help improving number guessing game
, but these inefficiencies build up in larger applications. This isn't premature optimization, but simply good coding style [ed: put in to fend off the premature optimization is bad puppets who infest this list]. Notice that the sequence of commands follows a logical sequence corresponding to decisions in the game. It makes the code more sensible, readable, and a little faster some times to boot. Good logic has the happy consequence of good speed most of the time. My code is typed real-time so is untested. No promise that there aren't typos but you will probably get the idea. But see if you can plug the these functions into the proper places and apply some of these techniques. James -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Need help improving number guessing game
James Stroud wrote: 1. Refactor. You should look at your code and see where you repeat the same or similar patterns, see where they differ, make functions, and make the differences parameters to the function call: def guess(player, p1score, p2score): guess1 = int(input(\n )) if guess1 100: print(ONLY NUMBERS FROM 1 TO 99) elif guess1 target: print(TOO HIGH) elif guess1 == target: print(GOOD JOB, PLAYER %s! THE SCORE IS: % player) print(P1: %s --- P2: %s % (p1score, p2score))) print(PLAY AGAIN?) #Set up the game again play = int(input(0 TO END: )) if play == 0: print(GOOD BYE. PLAY AGAIN SOON!) quit() else: target = random.randint(1, 99) else: print(TOO LOW) I realized this has a bug. The target is locked in the scope of the function. I wouldn't use global, though: def guess(player, p1score, p2score): target = None guess1 = int(input(\n )) if guess1 100: print(ONLY NUMBERS FROM 1 TO 99) elif guess1 target: print(TOO HIGH) elif guess1 == target: print(GOOD JOB, PLAYER %s! THE SCORE IS: % player) print(P1: %s --- P2: %s % (p1score, p2score))) print(PLAY AGAIN?) #Set up the game again play = int(input(0 TO END: )) if play == 0: print(GOOD BYE. PLAY AGAIN SOON!) quit() else: target = random.randint(1, 99) else: print(TOO LOW) Use it like this: new_target = gues(player, p1score, p2score) if new_target is not None: target = new_target I officially declare that I can't guarantee no more bugs in my previous post. I just fixed this one because my conscience was bothering me. James -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Need help improving number guessing game
I forgot to return target: def guess(player, p1score, p2score): target = None guess1 = int(input(\n )) if guess1 100: print(ONLY NUMBERS FROM 1 TO 99) elif guess1 target: print(TOO HIGH) elif guess1 == target: print(GOOD JOB, PLAYER %s! THE SCORE IS: % player) print(P1: %s --- P2: %s % (p1score, p2score))) print(PLAY AGAIN?) #Set up the game again play = int(input(0 TO END: )) if play == 0: print(GOOD BYE. PLAY AGAIN SOON!) quit() else: target = random.randint(1, 99) else: print(TOO LOW) return target -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Need help improving number guessing game
feba wrote: This is what I have so far. better? worse? Much better. I didn't check if it works. But you need to figure out a way to give up on your reliance on global variables. They will end up stifling you in the long run when you move to substantial projects. Also, you should start moving the nested if: then: blocks to functions. Finally, you should limit your lines to no more than 80 chars. I do 71. Don't be afraid to use transient variables to help. Be assured that it takes on special intelligence to write unintelligible code at will. Also be assured that fitting everything on one line is not a good way to save time. Aim for clarity. If you want to start off on the right foot, you'll grind on your guessing game until all variables are insulated within local scope and the logic of the program becomes apparent from its architecture as a collection of functions. This is an example of how to combine these concepts: def update_scores(player, p1sc, p2sc): if player == P1: plsc +=1 else: p2sc +=1 tmplt = CONGRATULATIONS %s! SCORE -- P1:%s P2:%s print(tmplt % (player, p1sc, p2sc)) return p1sc, p2sc p1sc, p2sc = update_scores(player, p1sc, p2sc) Finally, put comments on their own lines. Google python style guide. James -- http://mail.python.org/mailman/listinfo/python-list
Re: Need help improving number guessing game
James Stroud wrote: Be assured that it takes on special intelligence to write unintelligible I meant *no* special intelligence. -- http://mail.python.org/mailman/listinfo/python-list
Re: filter iterable based on predicate take from another iterable
Peter Otten wrote: [EMAIL PROTECTED] wrote: is there is a neat way to select items from an iterable based on predicates stored in another iterable without zipping? I can do something like this: import itertools foo = range(10) # select even numbers bar = map(lambda i: i%2, foo) foobarselected = itertools.ifilterfalse(lambda t: t[0], itertools.izip (bar,foo)) # for simplicity I want to work with the single item list, not the zipped one fooselected = list(t[1] for t in foobarselected) However, it would be nice to have a function combining the last two instructions. Something like itertools.ifilterother(bar, foo) - yield iterator with items from foo where bar is true I think it's a good approach to keep the number of primitives low. I find the list comprehension combined with izip() quite readable: [v for f, v in izip(bar, foo) if not f(v)] Peter If you want an iterator without requiring making a list, you can simply use parentheses instead of brackets: agenerator = (v for f, v in izip(bar, foo) if not f(v)) This is perfectly lazy but not immune to problems when foo or bar is changed before the generator is fully consumed. James -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
Re: How to pass out the result from iterated function
JD wrote: I got a iterated function like this: def iterSomething(list): has_something = False for cell in list: if something in cell: has_something = True output = something if has_something: iterSomething(output) else: final_out = outupt The problem is how can I read this final_out outside of the function. I tried the global statement, it seems not work. Any idea? JD I don't think this function will iterate the way you intend. You probably won't get many helpful suggestions until you define more precisely the nature of alist. Right now the function assumes single item lists only and will fail with an exception if something is not contained in the deepest list. E.g., only this type of situation is allowed: [[somethign]] or [[[something]]] or something etc. Anything else gives an exception. For example, this will fail with an exception: [[1,2,3], [4,5,6], [7,8,9]] Is that really what you want? Hint: you need to test whether you can iterate over the elements alist. Also, use something like alist and not list because list is a reserved word. James -- http://mail.python.org/mailman/listinfo/python-list
Re: internal circular class references
Ethan Furman wrote: Greetings List! I'm writing a wrapper to the datetime.date module to support having no date. Its intended use is to hold a date value from a dbf file, which can be empty. The class is functional at this point, but there is one thing I would like to change -- datetime.date.max and datetime.date.min are class attributes of datetime.date, and hold datetime.date values. At this point I have to have two lines outside the actual class definition to do the same thing, e.g.: trimmed down class code class NullDate(object): adds null capable DateTime.Date constructs __slots__ = ['_date'] def __new__(cls, date='', month=0, day=0): nulldate = object.__new__(cls) nulldate._date = . . . return nulldate def __getattr__(self, name): if self: attribute = self._date.__getattribute__(name) return attribute else: if callable(dt.date.__dict__[name]): return int else: return 0 def __nonzero__(self): if self._date: return True return False @classmethod def fromordinal(cls, number): if number: return cls(dt.date.fromordinal(number)) else: return cls() NullDate.max = NullDate(dt.date.max) NullDate.min = NullDate(dt.date.min) /trimmed down class code How can I move those last two lines into the class definition so that: 1) they are class attributes (not instance), and 2) they are NullDate type objects? ~ethan~ I resisted posting a similar question recently. After much consideration, I realized that the inability to reference a class inside its own definition must have been a deliberate design of the language. So the short answer is you can't. The way you have done it is best--its not a hack and is good style. James -- http://mail.python.org/mailman/listinfo/python-list
Re: Rich Comparisons Gotcha
Robert Kern wrote: James Stroud wrote: I think it skips straight to __eq__ if the element is not the first in the list. No, it doesn't skip straight to __eq__(). y is 1 returns False, so (y==1) is checked. When y is a numpy array, this returns an array of bools. list.__contains__() tries to convert this array to a bool and ndarray.__nonzero__() raises the exception. list.__contains__() checks is then __eq__() for each element before moving on to the next element. It does not try is for all elements, then try __eq__() for all elements. Ok. Thanks for the explanation. That no one acknowledges this makes me feel like a conspiracy is afoot. I don't know what you think I'm not acknowledging. Sorry. That was a failed attempt at humor. James -- http://mail.python.org/mailman/listinfo/python-list
Re: Brain going crazy with recursive functions
[EMAIL PROTECTED] wrote: I'm trying to solve the 9-tile puzzle using as functional an approach as possible. I've recently finished reading SICP and am deliberately avoiding easy python-isms for the more convoluted scheme/functional methods. The following function is trivial to do with for loops and directly accessing arrays with [] syntax. I'm trying to limit myself to the types of idioms/semantics one finds in minimal scheme, such as in SICP. I want eventually to port this to scheme, but I know python better, so that's where I'm starting. My current problem is the following. The 9-tile puzzle consists of a list of lists like this [[1,2,3],[4,5,6],[7,8,0]], where the numbers can be jumbled up. I'm looking for the location of the zero using *only* recursion and operators that are similar to car/cdr. The return value should be the row,col of the zero. For example above the return value would be (2,2). I'm also trying to define a single linear_search(...) function which does the search for within the row (an inner list above) and within the whole list. linear_search takes as an argument a truth_function which does the actual work. What's tricky is that the truth function for the array-as-a-whole is also the linear_search for a row. Once I'm in linear_search for the array, I also call linear_search for each row. The problem is the line where it says acc.insert(0,idx) looks fishy to me. It works fine and returns the row,col of the location of the zero tile, but it seems to be mutating a variable, and that's the thing I'm trying to avoid. In a sense, it's not hard enough and python is making this too easy :) (although it took a bit of mind-wrenching to get to this point. Recursion makes you either dumber or smarter, I'm not sure which). How do I accumulate the inner value of the search so it pops out at the end, without resorting to a mutable variable? I did a bit of search and the word monad came up, but I'm not sure what that is (I know it relates to haskell and some other purely functional stuff, but I get very lost when trying to read that stuff). def linear_search(array, truth_func, acc): # Goes through each element of array and applies truth_func. # Returns index if found, otherwise returns None def linear_search_iter(idx, truth_func, arr, acc): if arr: tf = truth_func(arr[0]) if tf or type(tf) is int: acc.insert(0,idx) return idx, acc+[idx] else: return linear_search_iter(idx+1, truth_func, arr[1:], acc) return linear_search_iter(0, truth_func, array, acc) def locate_zero(p): # Locates empty tile. Returns (r,c) tuple def find_zero_in_row(row): return linear_search(row, lambda x: x==0, acc) acc = [] ls = linear_search(p, find_zero_in_row, acc) print acc return acc thanks Michael I am honestly getting lost in your code. The following fulfills your requirements as far as I can tell. It uses None as a sentinel for the truth function matching no elements of the array. Some assignments are made within the code simply to make it more readable. They are not necessary. The first element that the truth function evaluates to True is returned. I hope it helps. James def linear_search(array, truth_func, loc=(0,0)): idx1, idx2 = loc if idx1 = len(array): return None if idx2 = len(array[idx1]): return linear_search(array, truth_func, (idx1+1, 0)) value = array[idx1][idx2] tf = truth_func(value) if tf: return loc else: return linear_search(array, truth_func, (idx1, idx2+1)) a = [[5, 3, 4], [2, 0, 1], [8, 6, 7]] linear_search(a, lambda x: x==0) -- http://mail.python.org/mailman/listinfo/python-list
Re: Brain going crazy with recursive functions
James Stroud wrote: def linear_search(array, truth_func, loc=(0,0)): idx1, idx2 = loc if idx1 = len(array): return None if idx2 = len(array[idx1]): return linear_search(array, truth_func, (idx1+1, 0)) value = array[idx1][idx2] tf = truth_func(value) if tf: return loc else: return linear_search(array, truth_func, (idx1, idx2+1)) a = [[5, 3, 4], [2, 0, 1], [8, 6, 7]] linear_search(a, lambda x: x==0) PS: If I just made it to easy for you, you can practice by generalizing this to an N-dimensional array using recursion. I'm tempted to do it myself but I'm going to try to resist instead and do some work that pays. -- http://mail.python.org/mailman/listinfo/python-list
Re: can graphs be made in python as we make in java
suku wrote: HI folks... i need some suggestion on making graphs. Will this be possible with normal python setup file or do i need to download add ons for that.. help me out I like pychart. It has the advantage of being pure python and makes very nice looking plots. You might also check out matplotlib if you are into heavyweight plotting and interactive application development. James -- http://mail.python.org/mailman/listinfo/python-list
Re: Rich Comparisons Gotcha
Rasmus Fogh wrote: Dear All, For the first time I have come across a Python feature that seems completely wrong. After the introduction of rich comparisons, equality comparison does not have to return a truth value, and may indeed return nothing at all and throw an error instead. As a result, code like if foo == bar: or foo in alist cannot be relied on to work. This is clearly no accident. According to the documentation all comparison operators are allowed to return non-booleans, or to throw errors. There is explicitly no guarantee that x == x is True. I'm not a computer scientist, so my language and perspective on the topic may be a bit naive, but I'll try to demonstrate my caveman understanding example. First, here is why the ability to throw an error is a feature: class Apple(object): def __init__(self, appleness): self.appleness = appleness def __cmp__(self, other): assert isinstance(other, Apple), 'must compare apples to apples' return cmp(self.appleness, other.appleness) class Orange(object): pass Apple(42) == Orange() Second, consider that any value in python also evaluates to a truth value in boolean context. Third, every function returns something. A function's returning nothing is not a possibility in the python language. None is something but evaluates to False in boolean context. But surely you can define an equal/unequal classification for all types of object, if you want to? This reminds me of complex numbers: would 4 + 4i be equal to sqrt(32)? Even in the realm of pure mathematics, the generality of objects (i.e. numbers) can not be assumed. James -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Rich Comparisons Gotcha
Luis Zarrabeitia wrote: Quoting James Stroud [EMAIL PROTECTED]: First, here is why the ability to throw an error is a feature: class Apple(object): def __init__(self, appleness): self.appleness = appleness def __cmp__(self, other): assert isinstance(other, Apple), 'must compare apples to apples' return cmp(self.appleness, other.appleness) class Orange(object): pass Apple(42) == Orange() I beg to disagree. The right answer for the question Am I equal to this chair right here? is not I don't know, nor I can't compare. The answer is No, I'm not a chair, thus I'm not equal to this chair right here. If someone comes to my house, looking for me, he will not run away because he sees a chair before he sees me. Your assert doesn't belong inside the methot, it should be up to the caller to decide if the human-chair comparisons make sense or not. I certainly don't want to be type-checking when looking for an object within a mixed-type collection. This reminds me of complex numbers: would 4 + 4i be equal to sqrt(32)? I assume you meant sqrt(32i). No, I definitely didn't mean sqrt(32i). I'm using sqrt() to represent the mathematical square root, and not an arbitrary function one might define, by the way. My point is that 4 + 4i, sqrt(32), and sqrt(-32) all exist in different spaces. They are not comparable, even when testing for equality in a pure mathematical sense. If when encounter these values in our programs, we might like the power to decide the results of these comparisons. In one context it might make sense to throw an exception, in another, it might make sense to return False based on the fact that we consider them different types, in yet another context, it might make sense to look at complex plane values as vectors and return their scalar magnitude for comparison to real numbers. I think this ability to define the results of comparisons is not a shortcoming of the language but a strength. -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Rich Comparisons Gotcha
Rasmus Fogh wrote:
Current behaviour is both inconsistent and counterintuitive, as these
examples show.
x = float('NaN')
x == x
False
Perhaps this should raise an exception? I think the problem is not with
comparisons in general but with the fact that nan is type float:
py type(float('NaN'))
type 'float'
No float can be equal to nan, but nan is a float. How can something be
not a number and a float at the same time? The illogicality of nan's
type creates the possibility for the illogical results of comparisons to
nan including comparing nan to itself.
ll = [x]
x in ll
True
x == ll[0]
False
But there is consistency on the basis of identity which is the test for
containment (in):
py x is x
True
py x in [x]
True
Identity and equality are two different concepts. Comparing identity to
equality is like comparing apples to oranges ;o)
import numpy
y = numpy.zeros((3,))
y
array([ 0., 0., 0.])
bool(y==y)
Traceback (most recent call last):
File stdin, line 1, in module
ValueError: The truth value of an array with more than one element is
ambiguous. Use a.any() or a.all()
But the equality test is not what fails here. It's the cast to bool that
fails, which for numpy works like a unary ufunc. The designers of numpy
thought that this would be a more desirable behavior. The test for
equality likewise is a binary ufunc and the behavior was chosen in numpy
for practical reasons. I don't know if you can overload the == operator
in C, but if you can, you would be able to achieve the same behavior.
ll1 = [y,1]
y in ll1
True
ll2 = [1,y]
y in ll2
Traceback (most recent call last):
File stdin, line 1, in module
ValueError: The truth value of an array with more than one element is
ambiguous. Use a.any() or a.all()
I think you could be safe calling this a bug with numpy. But the fact
that someone can create a bug with a language is not a condemnation of
the language. For example, C makes it real easy to crash a program by
overrunning the limits of an array, but no one would suggest to remove
arrays from C.
Can anybody see a way this could be fixed (please)? I may well have to
live with it, but I would really prefer not to.
Your only hope is to somehow convince the language designers to remove
the ability to overload == then get them to agree on what you think the
proper behavior should be for comparisons. I think the probability of
that happening is about zero, though, because such a change would run
counter to the dynamic nature of the language.
James
--
James Stroud
UCLA-DOE Institute for Genomics and Proteomics
Box 951570
Los Angeles, CA 90095
http://www.jamesstroud.com
--
http://mail.python.org/mailman/listinfo/python-list
Re: Rich Comparisons Gotcha
James Stroud wrote: [cast to bool] for numpy works like a unary ufunc. Scratch that. Not thinking and typing at same time. -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
Re: Rich Comparisons Gotcha
Steven D'Aprano wrote: On Sun, 07 Dec 2008 13:57:54 -0800, James Stroud wrote: Rasmus Fogh wrote: ll1 = [y,1] y in ll1 True ll2 = [1,y] y in ll2 Traceback (most recent call last): File stdin, line 1, in module ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all() I think you could be safe calling this a bug with numpy. Only in the sense that there are special cases where the array elements are all true, or all false, and numpy *could* safely return a bool. But special cases are not special enough to break the rules. Better for the numpy caller to write this: a.all() # or any() instead of: try: bool(a) except ValueError: a.all() as they would need to do if numpy sometimes returned a bool and sometimes raised an exception. I'm missing how a.all() solves the problem Rasmus describes, namely that the order of a python *list* affects the results of containment tests by numpy.array. E.g. y in ll1 and y in ll2 evaluate to different results in his example. It still seems like a bug in numpy to me, even if too much other stuff is broken if you fix it (in which case it apparently becomes an issue). James -- http://mail.python.org/mailman/listinfo/python-list
Re: Rich Comparisons Gotcha
Robert Kern wrote: James Stroud wrote: I'm missing how a.all() solves the problem Rasmus describes, namely that the order of a python *list* affects the results of containment tests by numpy.array. E.g. y in ll1 and y in ll2 evaluate to different results in his example. It still seems like a bug in numpy to me, even if too much other stuff is broken if you fix it (in which case it apparently becomes an issue). It's an issue, if anything, not a bug. There is no consistent implementation of bool(some_array) that works in all cases. numpy's predecessor Numeric used to implement this as returning True if at least one element was non-zero. This works well for bool(x!=y) (which is equivalent to (x!=y).any()) but does not work well for bool(x==y) (which should be (x==y).all()), but many people got confused and thought that bool(x==y) worked. When we made numpy, we decided to explicitly not allow bool(some_array) so that people will not write buggy code like this again. The deficiency is in the feature of rich comparisons, not numpy's implementation of it. __eq__() is allowed to return non-booleans; however, there are some parts of Python's implementation like list.__contains__() that still expect the return value of __eq__() to be meaningfully cast to a boolean. You have explained py 112 = [1, y] py y in 112 Traceback (most recent call last): File stdin, line 1, in module ValueError: The truth value of an array with more than one element is... but not py ll1 = [y,1] py y in ll1 True It's this discrepancy that seems like a bug, not that a ValueError is raised in the former case, which is perfectly reasonable to me. All I can imagine is that something like the following lives in the bowels of the python code for list: def __contains__(self, other): foundit = False for i, v in enumerate(self): if i == 0: # evaluates to bool numpy array foundit = one_kind_of_test(v, other) else: # raises exception for numpy array foundit = another_kind_of_test(v, other) if foundit: break return foundit I'm trying to imagine some other way to get the results mentioned but I honestly can't. It's beyond me why someone would do such a thing, but perhaps it's an optimization of some sort. James -- http://mail.python.org/mailman/listinfo/python-list
Re: Rich Comparisons Gotcha
Robert Kern wrote: James Stroud wrote: py 112 = [1, y] py y in 112 Traceback (most recent call last): File stdin, line 1, in module ValueError: The truth value of an array with more than one element is... but not py ll1 = [y,1] py y in ll1 True It's this discrepancy that seems like a bug, not that a ValueError is raised in the former case, which is perfectly reasonable to me. Nothing to do with numpy. list.__contains__() checks for identity with is before it goes to __eq__(). ...but only for the first element of the list: py import numpy py y = numpy.array([1,2,3]) py y array([1, 2, 3]) py y in [1, y] Traceback (most recent call last): File ipython console, line 1, in module type 'exceptions.ValueError': The truth value of an array with more than one element is ambiguous. Use a.any() or a.all() py y is [1, y][1] True I think it skips straight to __eq__ if the element is not the first in the list. That no one acknowledges this makes me feel like a conspiracy is afoot. -- http://mail.python.org/mailman/listinfo/python-list
Re: Guido's new method definition idea
Steven D'Aprano wrote: On Fri, 05 Dec 2008 20:35:07 -0800, James Stroud wrote: Daniel Fetchinson wrote: I'd like this new way of defining methods, what do you guys think? Consider the maverick who insists on class C: def me.method(arg): self.value = arg Replace self with me. Yes, I corrected myself one minute after I made the typo. which should be equivalent to class C: def method(me, arg): me.value = arg What's the interpreter going to do with our maverick's code? I don't see why you think this is a problem. The behavior was unspecified as far as I could tell and I was curious as to whether me would still be allowed as a reference to self. Allowing alternatives to self would maintain backwards compatibility as the use of self has been a convention and not enforced by the language. James -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
Re: operators as variables
macc_200 wrote:
Hi,
just starting programming and have an elementary question after
playing around with lists but cannot find the answer with googling.
I have a list of variables and I would like some of those variables to
be integers and some to be operators so the list would look something
like [5 * 4 - 4 + 6] and then be able to evaluate the result (i.e. get
10). How do you make the interpreter see the operator as that instead
of a string and just echo the list back to me.
Your specification is ambiguous because you mention lists but wrote an
evaluable expression inside of brackets. Others have answered the
question you probably really are asking. For fun, though, I'm going to
pretend you meant list and not whatever [5 * 4 - 4 + 6] is:
import operator
opdict = {'+' : operator.add,
'-' : operator.sub,
'*' : operator.mul,
'/' : operator.div}
def take_two(aniterable):
assert len(aniterable) % 2 == 0
aniter = iter(aniterable)
while True:
try:
yield aniter.next(), aniter.next()
except StopIteration:
break
def reductifier(alist):
value = alist.pop(0)
for op, operand in take_two(alist):
value = opdict[op](value, operand)
return value
reductifier([5, *, 4, -, 4, +, 6])
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dict subclass and pickle bug (?)
Hello All, I subclassed dict and overrode __setitem__. When instances are unpickled, the __setstate__ is not called before the keys are assigned via __setitem__ in the unpickling protocol. I googled a bit and found that this a bug filed in 2003: http://bugs.python.org/issue826897 It is still open with normal priority. Am I missing something? Is there a workaround for this bug that makes fixing it pointless or has it just fallen through the cracks for the last 5 years? Here is an example: class DictPlus(dict): def __init__(self, *args, **kwargs): self.extra_thing = ExtraThingClass() dict.__init__(self, *args, **kwargs) def __setitem__(self, k, v): do_something_with(self.extra_thing, k, v) dict.__setitem__(self, k, v) Upon unpickling, the error would be: AttributeError: 'DictPlus' object has no attribute 'extra_thing' I'm still using python 2.5.1. James -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
Re: dict subclass and pickle bug (?)
James Stroud wrote: Hello All, I subclassed dict and overrode __setitem__. When instances are unpickled, the __setstate__ is not called before the keys are assigned via __setitem__ in the unpickling protocol. I googled a bit and found that this a bug filed in 2003: http://bugs.python.org/issue826897 It is still open with normal priority. Here is the ugly fix I'm basically going to have to live with, it seems: class DictPlus(dict): def __init__(self, *args, **kwargs): self.extra_thing = ExtraThingClass() dict.__init__(self, *args, **kwargs) def __setitem__(self, k, v): try: do_something_with(self.extra_thing, k, v) except AttributeError: self.extra_thing = ExtraThingClass() do_something_with(self.extra_thing, k, v) dict.__setitem__(self, k, v) def __setstate__(self, adict): pass This violates this: Beautiful is better than ugly. I can't imagine this bug has survived but I also can't imagine any better way to do this without specifying a different protocol, which would probably break other pickling I'm doing. I don't feel like finding out right now. Maybe repeal pep 307 ;o) James -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
Re: To Troll or Not To Troll (aka: as keyword woes)
Andreas Waldenburger wrote: Is it me, or has c.l.p. developed a slightly harsher tone recently? (Haven't been following for a while.) Yep. I can only post here for about a week or two until someone blows a cylinder and gets ugly because they interpreted something I said as a criticism of the language and took it personally by extension. Then I have to take a 4 month break because I'm VERY prone to reciprocating--nastily. I think its a symptom of the language's maturing, getting popular, and a minority fraction* of the language's most devout advocates developing an egotism that complements their python worship in a most unsavory way. I wish they would instead spend their energy volunteering to moderate this list and culling out some of the spam. *No names were mentioned in the making of this post. -- http://mail.python.org/mailman/listinfo/python-list
Re: dict subclass and pickle bug (?)
Terry Reedy wrote: because there is no bug to fix. I have suggesting closing. May I suggest to add something to this effect within the issue itself so others won't spend time trying to figure out why the bug is still open? If this is a more general feature of issues, then perhaps it would be helpful to provide a footnote at the bottom of all issue pages via the page template that explains why they are not bugs and suggests a general course of action for the programmer. James -- http://mail.python.org/mailman/listinfo/python-list
Re: dict subclass and pickle bug (?)
James Stroud wrote: Terry Reedy wrote: because there is no bug to fix. I have suggesting closing. May I suggest to add something to this effect within the issue itself so others won't spend time trying to figure out why the bug is still open? Sorry, you did that. James -- http://mail.python.org/mailman/listinfo/python-list
Re: To Troll or Not To Troll (aka: as keyword woes)
alex23 wrote: On Dec 6, 8:00 am, James Stroud [EMAIL PROTECTED] wrote: I think its a symptom of the language's maturing, getting popular, and a minority fraction* of the language's most devout advocates developing an egotism that complements their python worship in a most unsavory way. It's hard to see how anyone could ever take offence at your posts given such unbiased objectivity ;) I know you are winking, but I literally keep a sock stuffed in my mouth at work to keep my own python advocacy at bay so I can get some work done and not drive my coworkers crazy. -- http://mail.python.org/mailman/listinfo/python-list
Re: Guido's new method definition idea
Daniel Fetchinson wrote: http://neopythonic.blogspot.com/2008/10/why-explicit-self-has-to-stay.html The proposal is to allow this: class C: def self.method( arg ): self.value = arg return self.value instead of this: class C: def method( self, arg ): self.value = arg return self.value I'd like this new way of defining methods, what do you guys think? Consider the maverick who insists on class C: def me.method(arg): self.value = arg which should be equivalent to class C: def method(me, arg): me.value = arg What's the interpreter going to do with our maverick's code? James -- http://mail.python.org/mailman/listinfo/python-list
Re: Guido's new method definition idea
Of course I meant class C: def me.method(arg): me.value = arg James -- http://mail.python.org/mailman/listinfo/python-list
Re: How can I do this (from Perl) in Python? (closures)
[EMAIL PROTECTED] wrote: from_ten = make_counter(10) from_three = make_counter(3) print from_ten() # 10 print from_ten() # 11 print from_three() # 3 print from_ten() # 12 print from_three() # 4 The error message is: UnboundLocalError: local variable 'start' referenced before assignment. The same thing happens if I omit start and just use start_num directly. How can I do it in Python? Since no one has suggested it: class make_counter(object): def __init__(self, i): self.i = i def __call__(self): i = self.i self.i += 1 return i James -- James Stroud UCLA-DOE Institute for Genomics and Proteomics Box 951570 Los Angeles, CA 90095 http://www.jamesstroud.com -- http://mail.python.org/mailman/listinfo/python-list
