Creating instances of untrusted new-style classes
Is there any safe way to create an instance of an untrusted class
without consulting the class in any way? With old-style classes, I can
recreate an instance from another one without worrying about malicious
code (ignoring, for now, malicious code involving attribute access) as
shown below.
import types
class Foo:
... def __init__(self, who, knows, what, args):
... self.mystery_args = (who, knows, what, args)
... print Your code didn't expect the Spanish inquisition!
...
f = Foo('spam','eggs','ham','bacon') # This would be in a restricted
environment, though.
Your code didn't expect the Spanish inquisition!
types.InstanceType(Foo, f.__dict__) # This wouldn't, but we never run that
code, anyways.
__main__.Foo instance at 0x008B5FD0
I'm not sure how to do the same for new-style classes, if it's at all
possible to do from within Python. Is there any way to accomplish this,
or is there no practical way to do so?
Thanks,
- Devan
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Re: Creating instances of untrusted new-style classes
Ben Finney wrote: Devan L [EMAIL PROTECTED] writes: Is there any safe way to create an instance of an untrusted class Why are you instantiating classes you don't trust? without consulting the class in any way? If you don't consult the class, how can the instance be created properly? When my program runs (CGI), the following happens: * User enters source, which is executed in a restricted environment, which unserializes a previously serialized environment if there is one. * The restricted environment is serialized, including any instances they may have instantiated. So when I unserialize their instances, I have to recreate them, but without calling any of their code (I can't run the unserializing code in a restricted environment). Instances of old-style classes can be created without touching the actual old-style class code, but I'm not sure how, if it's possible, to do the same with new-style classes - Devan -- http://mail.python.org/mailman/listinfo/python-list
Re: Creating instances of untrusted new-style classes
Michael Spencer wrote:
Devan L wrote:
Is there any safe way to create an instance of an untrusted class
without consulting the class in any way? With old-style classes, I can
recreate an instance from another one without worrying about malicious
code (ignoring, for now, malicious code involving attribute access) as
shown below.
[snip my example]
I'm not sure how to do the same for new-style classes, if it's at all
possible to do from within Python. Is there any way to accomplish this,
or is there no practical way to do so?
Thanks,
- Devan
class A(object):
... def __init__(self, *args):
... self.args = args
... print Calling __init__
...
a = A(new,style)
Calling __init__
b = object.__new__(A)
b.__dict__ = a.__dict__.copy()
b.args
('new', 'style')
type(a) is type(b)
True
HTH
Michael
Thanks, now I just have to figure out all the meddling small details I
put off before!
-Devan
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Re: Safe Python Execution
Graham wrote:
I've been messing around with trying to get a small sandbox like
environment where i could execute python code in a safe way.
Basically what the old restricted execution module attempted to do.
I've written a small amount of code to get custom interpreter running,
but i'm not really sure if its safe.
The way i'm controlling functionality is with some games and exec, so
if 'code' was the text code you wanted to execute i run:
exec code in {'__builtins__':None}
obviously this doesn't give you much to play with, but it does remove
file access and importing as far as i can tell. Can anyone think of a
hack around this? I assume if it was this easy it would be a module
already but i figured i would ask.
You need to remove reload, replace __import__, disable __subclasses__
(not convenient nor portable because you need to do it in the source.
Shouldn't it be restricted in restricted mode?). That removes most
glaring security holes, I think. If you need to touch any of the
attributes of the objects in the sandbox, you might want to remove
properties. I wouldn't recommend exposing any objects outside of the
sandbox to the sandbox, either.
Zope also has some cool viral proxy thing that I don't understand that
you might want to look into.
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(Different) Try Python Update
It's been a while since I've done anything, and I have finals, so if anyone wants to look at some of the source, here's the somewhat cleaned up source for bastille and modjelly. Bastille is just a sort-of-more-secure equivalent of what the code module is, in case you have no clue what it does since I haven't really mentioned it. Bastille: http://www.datamech.com/devan/bastille.py.txt Modjelly: http://www.datamech.com/devan/modjelly.py.txt On a side note, I just realized that due to some bug, any function definition after the first function is defined simply binds the name to the first one, which is a very bad thing! So if you can find anything related to this in the source, send me an email. Oh, right, and in case you have no clue what I'm talking about, I'm trying to replicate an interactive session online. My Try Python is at http://www.datamech.com/devan/trypython/trypython.py and Mike Meyer's cooler one is at http://www.mired.org/home/mwm/try_python/. -- http://mail.python.org/mailman/listinfo/python-list
Re: Try Python update
Mike Meyer wrote: Xavier Morel [EMAIL PROTECTED] writes: [Old message and Xavier's question] [Mike's reply to Xavier] Since Python doesn't have any way to secure the interface built-in, i'd be interrested in that. Devan apparently doesn't have as cooperative an ISP, and is working on securing the interpreter. What he's done may be more interesting. It's not particularily interesting. The C code simply has more attributes restricted in restricted mode, disabling in particular __subclasses__. The rest is creating safe __builtins__ and only giving them some modules (but again, importing is still largely broken, although one liners are still possible). In any case, I don't know how secure it actually is, since nobody seems to go further than import os or import sys. So if you're bored, you can try to break into it. I haven't secured modjelly entirely, and it might be possible to trick modjelly into executing code by using descriptors when it tries to pull out all of the information. Then again, I haven't even added support for properties in it yet. Plus it has no support for if you delete critical attributes which are needed to recreate the object. Still, I think it's good enough to deter any random person from trying to wipe the server for now. -- http://mail.python.org/mailman/listinfo/python-list
Re: Try Python update
[EMAIL PROTECTED] wrote: I like the form, no matter what its limitations may be. Three notes: It might be a good way to catch newbi mistakes (those are the kind I make :P, thereby providing a feedback loop to improved error messages. I had no trouble with from math import * followed by print pi, but there was no prompt after the result appeared .. is that part of the 'closures' thing mentioned earlier? Then I followed you type 'help' suggestion, which had me in stitches (sorry, it's been a long day and the Knob Creek was kicking in) -- I got exactly the message you'd expect, about help not being recognized and maybe help() would work. That's what triggered the idea for trapping errors. Nice work! George Uh, I'm messing with import right now, but essentially, I wouldn't recommend importing (one line __import__ hacks only!) or printing. -- http://mail.python.org/mailman/listinfo/python-list
Re: Try Python update
Mike Meyer wrote: [EMAIL PROTECTED] writes: [comments about Mike Meyer's try python, I think] I had no trouble with from math import * followed by print pi, but there was no prompt after the result appeared .. is that part of the 'closures' thing mentioned earlier? Hmm. Are you looking at mine URL: http://www.mired.org/home/mwm/try_python/ , or Devans URL: http://www.datamech.com/devan/trypython/trypython.py ? Mine doesn't handle code (though he's provide pointers I plan on using to make it do so). I think he said his has problems with closures. I'm renaming mine to the Python Online REPL or Online Python REPL, whichever you prefer, to help differentiate from Mike's. From the actual recipe: http://www.onlamp.com/python/pythoncook2/solution.csp?day=2 (The url changes every day as they move it one day back) if co.co_freevars or co.co_cellvars: raise ValueError, Sorry, cannot pickle code objects from closures I think that the code constructor (types.CodeType) doesn't take co_freevars or co_cellvars as an arg, so I can't directly create a new code object from the attribute of the old one with co_freevars and co_cellvars. I might be able to set the attributes after,but I'll have to test it out to see. Then I followed you type 'help' suggestion, which had me in stitches (sorry, it's been a long day and the Knob Creek was kicking in) -- I got exactly the message you'd expect, about help not being recognized and maybe help() would work. That's what triggered the idea for trapping errors. Hmm. help seems to work fine in both of them. license() fails the same way in both of them (it tries to read from stdin, so), which means that you can probalby make help fail on them both if you work at it. Printing and most things not explicitly called by my code isn't done correctly (strings to lines to strings again!), so most any printing non-single statements or input will probably break it. -- http://mail.python.org/mailman/listinfo/python-list
Re: Try Python update
Mike Meyer wrote:
After spending time I should have been sleeping working on it, the try
python site is much more functional. It now allows statements,
including multi-line statements and expressions. You can't create code
objects yet, so it's still more a programmable calculator than
anything real.
I've got some of the tutorial text (literally) up as well. I hope to
make it easier to read the tutorial and interact with python at the
same time in the near future.
The url is http://www.mired.org/home/mwm/try_python/. Reports of
problems would appreciated.
If you want to try an online P{ython tool that lets you save code, try
Devan L's at http://www.datamech.com/devan/trypython/trypython.py.
My code uses one of the recipes from the Python Cookbook, 7.6 Pickling
Code Objects. It's limited to closures though, just like in the recipe.
So uh, you can't write closures in mine.
On a side note, my brother has tinkered with the C internals and now
__subclasses__ is restricted and many, many os and posix commands are
restricted (not that you can get them anyways, since importing is
broken!)
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Re: Try Python update
Mike Meyer wrote:
Devan L [EMAIL PROTECTED] writes:
If you want to try an online P{ython tool that lets you save code, try
Devan L's at http://www.datamech.com/devan/trypython/trypython.py.
My code uses one of the recipes from the Python Cookbook, 7.6 Pickling
Code Objects. It's limited to closures though, just like in the recipe.
So uh, you can't write closures in mine.
I don't have the dead trees version, and the online version doesn't
have chapter numbers. Is that URL:
http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/212565?
It was one of the recipes of the day, actually. They don't keep them up
for more than a week, though, I think. But more or less it has all of
the attributes used for creating an object from types.CodeType in
correct order.
On a side note, my brother has tinkered with the C internals and now
__subclasses__ is restricted and many, many os and posix commands are
restricted (not that you can get them anyways, since importing is
broken!)
I got import to work by pickling pairs of names - the variable name
that references the module, and the name of the module. When it
unpickles the list, it reimports them and points the appropriate
variable at them. This had unwanted effects if you did an import
this. It also doesn't work for objects that contain references to
modules.
My general method of storing is to store everything possible. See a
function? Store the function object itself. See a class? Store the
class object. Unfortunately, I can't store builtin methods or
functions, so this breaks on most modules. Don't try to reference the
__builtins__, by the way, otherwise it won't be removed and modjelly
will break.
I tried for a bit to restrict things, then gave up and did it
externally. There's no access to any files but those required to run
the script that deals with thing, and some other python modules that I
decided would be nice to have. Normally, nothing in the tree is
writable, either. Once I'm happy with it, I'll save a copy of the tree
somewhere and set up a cron job to refresh it at regular intervals.
I don't have enough control on the server to effectively restrict it
externally (no running as an unprivelleged user!), so I have to lock it
down as tightly as possible internally.
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ANN: (Different) Try Python Beta
I've spent a while putting together a partially working Try Python which handles class and function definitions. It also (used to) work with imports, but my hacked version of jelly doesn't work with it anymore, so only import this works as far as I know. It won't play nice if you store the id of an object because the objects are recreated every time, but references still work. It also won't let you maintain generators or iterators, but you can still put them inside functions to use. Printing also adds unnecessary newlines which I haven't fixed yet. And no, it doesn't use AJA(X|T), only some javascript to focus the input box. So here's the link for it: http://www.datamech.com/devan/trypython/trypython.py And if you want to see Mike Meyers' nicer, original one: http://www.mired.org/home/mwm/try_python/ If you want to see the source, send me an email, although you may have to gouge your eyes out after reading it. -- http://mail.python.org/mailman/listinfo/python-list
Re: ANN: (Different) Try Python Beta
Steve Holden wrote: Devan L wrote: [what I said] At first I thought 'the cgitb TypeError message from import os is impressively drastic :-)'. Then I realised in a later session that import os only gave an error message after I'd run import this. Thereafter, unfortunately, almost any input - legal or not - appears to result in a cgitb trace. Try reloading the page, otherwise it will use the old session id. It likes to break one step input after the offending action. It will also screw up the state of the session. Incidentally, import this doesn't seem to work, either. But importing is broken in general anyways, so I wouldn't recommend using it. -- http://mail.python.org/mailman/listinfo/python-list
Re: ANNOUNCE; Try python beta
Mike Meyer wrote: Ok, I've given it the interface I want, and made it less of an attractive nuisance. http://www.mired.org/home/mwm/try_python/ is now ready for people to play with. There's no tutorial information on it yet, that's the next thing to do. However, I won't be able to work on it for a while, so if you want to make suggestions about what that should look like, all such suggestions will be given proper consideration. I was bored so I wrote some code that takes input one line at a time and spits out the a tuple representing the state and a message to be echoed. It handles statements on multiple lines, too. So it might be helpful, since your tutorial doesn't seem to handle multiple lines or statements. You can see it at http://www.datamech.com/devan/bastille.txt -- http://mail.python.org/mailman/listinfo/python-list
Re: CGI module does not parse data
amfr wrote: I am writing a webserver, and I want it to be able to run python scripts. But when I set sys.stdin to self.rfile (using the BaseHTTPServer class, self.rfile is a input stream containing the request), the cgi module does not parse the data. Example script: import cgi form = cgi.FieldStorage() print form[testfield] The above script would print nothing. Should i be setting sys.stdin to something else, or is there anthoer solution entirely? try this before trying to print: print Content-Type: text/html\n -- http://mail.python.org/mailman/listinfo/python-list
Re: slice notation as values?
Antoon Pardon wrote: On 2005-12-10, Duncan Booth [EMAIL PROTECTED] wrote: [snip] I also think that other functions could benefit. For instance suppose you want to iterate over every second element in a list. Sure you can use an extended slice or use some kind of while. But why not extend enumerate to include an optional slice parameter, so you could do it as follows: for el in enumerate(lst,::2) 'Why not'? Because it makes for a more complicated interface for something you can already do quite easily. Do you think so? This IMO should provide (0,lst[0]), (2,lst[2]), (4,lst[4]) ... I haven't found a way to do this easily. Except for something like: start = 0: while start len(lst): yield start, lst[start] start += 2 But if you accept this, then there was no need for enumerate in the first place. So eager to learn something new, how do you do this quite easily? lst = ['ham','eggs','bacon','spam','foo','bar','baz'] list(enumerate(lst))[::2] [(0, 'ham'), (2, 'bacon'), (4, 'foo'), (6, 'baz')] No changes to the language necessary. -- http://mail.python.org/mailman/listinfo/python-list
Re: join dictionaries using keys from one values
ProvoWallis wrote:
Thanks so much. I never would have been able to figure this out on my
own.
def dictionary_join(one, two):
dict2x = dict( ((dict2[k], k) for k in dict2.iterkeys()))
dict3 = dict(((k, dict2x[v]) for k,v in dict1.iteritems()))
print dict3
dict1 = {1:'bbb', 2:'aaa', 3:'ccc'}
dict2 = {'5.01':'bbb', '6.01':'ccc', '7.01':'aaa'}
dictionary_join(dict1, dict2)
You might want to make a working function.
def join_dicts(d1,d2):
temp = dict(((d2[k], k) for k in d2.iterkeys()))
joined = dict(((k, temp[v]) for k,v in d1.iteritems()))
return joined
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Re: what's wrong with lambda x : print x/60,x%60
Steve Holden wrote: [EMAIL PROTECTED] wrote: Gary Herron [EMAIL PROTECTED] wrote in message news:[EMAIL PROTECTED] --snip-- So just use a def. It is constantly pointed out on this list that the lambda provides no extra expressive power, it is merely a shortcut No, it is not merely a shortcut. It often allows one to avoid polluting the namespace with a completely superfluous function name, thus reducing code smell. It can also avoid a multi-line function defintion which often pushes other relevant code off the current page and out of view, and thus lambda can increase program readability. I'm getting a little tired of namespace pollution being trotted out as a reason to use lambda. Defining a function, and giving it a name, isn't polluting the namespace, any more than assigning sub-expressions to temporary variables is polluting the namespace. Why use temporary variables when all you have to do is make your expressions three lines long to avoid polluting the namespace? I agree, if I were to name my function `shuffle', then I wouldn't be able to name any of my intermediate functions `shuffle'! Oh the humanity! Therefore I will instead use adhere to my 0 namespace pollution policy and use this instead: __nopollution_at__all_portion = range(50) __nopollution_at__all_word = 'mint white chocolate chip' if __name__ == '__main__': print (lambda portion,word:(lambda x,word:[x.pop() for i in range(len(word))]+x)((lambda x,word:[x.pop() for i in range(len(word))]+x)((lambda x,word:[x.pop() for i in range(len(word))]+x)((lambda x,word:[x.pop() for i in range(len(word))]+x)(portion[:],word),word),word),word))(__nopollution_at__all_portion,__nopollution_at__all_word) ;-) -- http://mail.python.org/mailman/listinfo/python-list
Re: Recursion bug...
ex_ottoyuhr wrote: To start with, I'm new at Python, so if this is something relatively ordinary or a symptom of thinking in C++, I apologize... Anyhow, I'm currently trying to write a means of generating genetic-programming functions in Python; the details would be a little much for a Usenet post, but suffice it to say that it would involve trees of objects with an opcode and a variable number, between in this case 0 and 3, of 'arguments' -- also objects of the same sort. As a function to implement them, I'm doing something to the effect of this: [ex_ottoyuhr's code] Sorry to have given such a long example... But anyways, the problem is that, while I think this should generate a number of children for each toRet equivalent to the required number of children, it's actually appending all children generated in the function to the 'root' toRet rather than to child functions -- so that if I ask for a tree with depth 2, and the root would have 2 arguments, the first child would have 1, and the second child would have 2, the result is a root with a 5-argument-long children and two child functions with 0-argument ones. There's some other strange stuff going on here, too; in particular, with one particular opcode, toRet is assigned a member 'value' which is randomly generated between 0 and 10,000. All toRets assigned value seem to be ending up with the same result... Could anyone explain what I'm doing wrong? I'm beginning to suspect that Python scope rules must not work like my native C++; have I made a common mistake? Well, for one, in your __init__ method, you never do anything with anOpcode. You simply assign the name 'opcode' to anOpcode. The reason why everything is the same is that you're accessing TreeCommand.children or Treecommand.opcode, which is shared by all instances unless you assign to it. And you never increment generated, so I don't see why the while loop would ever end, unless you intentionally wanted that. Try this code instead: max_opcode = 20 max_with_args = 15 class TreeCommand: def __init__(self, opcode) : self.opcode = opcode self.children = [] def MakeTreeCommand(depth, maxdepth) : if depth == 0: command = TreeCommand(random.randint(0, max_with_args) elif depth == maxdepth: command = TreeCommand(random.randint(max_with_args+1, max_opcode)) else: command = TreeCommand(random.randint(0, max_opcode)) if command.opcode = max_with_args: children_required = something_greater_than_0 else: children_required = 0 generated = 0 for i in range(children_required): command.children.append(MakeTreeCommand(depth+1, maxdepth)) return command -- http://mail.python.org/mailman/listinfo/python-list
Re: XUL behavior in Python via XPCOM, Mozilla
Terry Hancock wrote: I recently saw a claim that Mozilla XUL behaviors (normally scripted in Javascript) can (or perhaps will) be scriptable in Python. Also, other languages such as Java or Python are supported through XPCOM, said about Mozilla (from Luxor website). Yes, I know several ways to *generate* XUL from Python, and at least one way to use XUL to create interfaces for Python programs, but in this case, I'm talking about defining button action behavior in XUL by calling Python scripts. I know that Javascript is the preferred language, but I've seen several references to being able to do this in Python, including a claim that a release was targeted for early November (2005), to provide this. Now I can't find it again. Anyway, I was hoping someone on c.l.p / python.org would have a reliable reference on this. Thanks, Terry -- Terry Hancock ([EMAIL PROTECTED]) Anansi Spaceworks http://www.AnansiSpaceworks.com Nufox? http://trac.nunatak.com.au/projects/nufox -- http://mail.python.org/mailman/listinfo/python-list
Re: Command-line tool able to take multiple commands at one time?
Peter A. Schott wrote: OK - I justed tested and may be doing something wrong, but it didn't work when I just tried it. I have something like this: X = Value1 Y = Value2 Z = Value3 etc at the top of my script. When I copy/paste those three lines all at once into IDLE's interactive window, X is defined, Y and Z are not. That's more the behaviour I was hoping for - the ability to run parts of my code at a time in order to work through issues without too much trouble in mostly-working code. TIA, -Pete Schott Oh, that kind of multi-line input. I thought you were talking about def foo(bar): ...long_statement_here ...even_longer_statement_here ...return something I would just put it into a .py and run it through IDLE, change it, and rerun it. There are probably other IDEs which can already do that, but I just use IDLE. -- http://mail.python.org/mailman/listinfo/python-list
Re: Command-line tool able to take multiple commands at one time?
Peter A. Schott wrote: Per subject - I realize I can copy/paste a line at a time into an interactive session when I'm trying to debug, but was wondering if there is any tool out there that allows me to copy sections of working Python scripts to paste into my interactive console and let those run so I don't have to copy line-by-line. Not sure if iPython would meet that criteria or not or even if such a beast exists. It would be helpful for debugging some of my simpler, yet still lengthy at times, scripts. Thanks in advance. -Pete Schott It's called IDLE (At least, the interactive session with it). Some people dislike IDLE, though. -- http://mail.python.org/mailman/listinfo/python-list
Re: Underscores in Python numbers
Gustav Hållberg wrote: I tried finding a discussion around adding the possibility to have optional underscores inside numbers in Python. This is a popular option available in several competing scripting langauges, that I would love to see in Python. Examples: 1_234_567 0xdead_beef 3.141_592 Would appreciate if someone could find a pointer to a previous discussion on this topic, or add it to a Python-feature-wishlist. - Gustav I'm not sure what the _s are for, but I'm guessing they serve as separators (. or , depending on where you're from). I think the _s look ugly to me, besides, underscores look more like spaces than separators. -- http://mail.python.org/mailman/listinfo/python-list
Re: Cheapest pocket device to code python on
[EMAIL PROTECTED] wrote: What is the cheapest/affordable pocket device that I can code python on? I think the closest I have seen is pocketpc from this page: http://www.murkworks.com/Research/Python/PocketPCPython/Overview I would not recommend trying to code on a handheld device. Small screen size and [usually] small keyboards make it less-than-practical. Stick with a laptop, or write it in a notebook, if you must. -- http://mail.python.org/mailman/listinfo/python-list
Re: Importing Modules
Sam Pointon wrote:
On the second point, a combination of sys.path, os.listdir and
__import__ should do what you're after, although sifting through the
whole of sys.path and subfolders from Python, rather than the
interpreter itself, could be slow. (And it'll be redundant as well -
__import__ will have do the same thing, though you could fix that by
using the imp module).
-Should- work, but not tested, so don't blame me if it doesn't:
[code]
__import__(modulename) is not equivalent to import modulename;
__import__ returns a module object
__import__('pickle')
module 'pickle' from 'E:\Python23\lib\pickle.py'
pickle
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Re: Importing at runtime
http://www.python.org/doc/2.4.2/lib/built-in-funcs.html or, if you want an answer in code now and don't want to read the docs def my_import(name): module = __import__(name) globals()[name] = module #not a good idea Or, seeing as how you won't be directly accessing them by name, anyways modules = [__import__(name) for name in module_names] -- http://mail.python.org/mailman/listinfo/python-list
Re: execution order in list/generator expression
[EMAIL PROTECTED] wrote: Hi, I am wondering how this is evaluated. a=(x for x in [1,2,3,4]) p=[4,5] c=[x for x in p if x in list(a)] c is [] but if I expand a first, like a = list(a) c is [4] So it seems that the if part don't get expanded ? Well, for every element in p it recalculates list(a). Since the generator is exhausted after making a list from it, it gives you nothing afterwards. So after it checks the first element, it's equivalent to [x for x in p if x in []]. -- http://mail.python.org/mailman/listinfo/python-list
Re: Character Sequence Generation
Jeff Schwab wrote: [EMAIL PROTECTED] wrote: Jeff Schwab wrote: What's the best way to generate a sequence of characters in Python? I'm looking for something like this Perl code: 'a' .. 'z' . import string print string.ascii_lowercase abcdefghijklmnopqrstuvwxyz Thanks. Is there a good way to generate the characters dynamically? ''.join([chr(i) for i in range(97,123)]) -- http://mail.python.org/mailman/listinfo/python-list
Re: Newbie - instanciating classes from other files
[EMAIL PROTECTED] wrote: Hey guys, i just started learning python (i usually use java/C). this has got me stumped as its not mentioned in the documentation (unless im skimming it every time). How does one instanciate a class from another file import somefile foo = somefile.class(__init__arguments-should-go-here) Don't include the .py, it's won't work. -- http://mail.python.org/mailman/listinfo/python-list
Re: infinite loop
LOPEZ GARCIA DE LOMANA, ADRIAN wrote: Hi all, I have a question with some code I'm writting: def main(): if option == 1: function_a() elif option == 2: function_b() else: raise 'option has to be either 1 or 2' if iteration == True: main() def function_a(): print 'hello from function a' return None def function_b(): print 'hello from function b' return None iteration = True option = 1 main() I want an infinite loop, but after some iterations (996) it breaks: [EMAIL PROTECTED] tmp]$ python test.py hello from function a hello from function a hello from function a . . . hello from function a hello from function a Traceback (most recent call last): File test.py, line 35, in ? main() File test.py, line 17, in main main() File test.py, line 17, in main . . . . File test.py, line 17, in main main() File test.py, line 17, in main main() File test.py, line 5, in main function_a() RuntimeError: maximum recursion depth exceeded I don't understand it. Why am I not allowed to iterate infinitely? Something about the functions? What should I do for having an infinite loop? Thanks in advance for your help, Adrián. You've written a recursive function-you're not iterating. The recursion limit is there to keep you from making something which will do something bad, like recurse cyclically. -- http://mail.python.org/mailman/listinfo/python-list
Re: Python compiled?
billiejoex wrote: Hi all. I'm sorry for a noob question like this but I'll try to ask it anyway. One of the greatest problem that may discourage a new user to choose Python language is it's interpreted nature. What? The instant gratification of immediate results is not discouraging. Another important problem is that no interpreter is installed on Windows machine by default and this makes harder to distribute the software. Python isn't that big to install, and people don't have problems with small downloads Does it is planned that, in a far future, Python will implement a form of compilation? This would be awesome. Again, I don't see how compiling would make Python better. -- http://mail.python.org/mailman/listinfo/python-list
Re: 'isa' keyword
talin at acm dot org wrote: Thanks for all the respones :) I realized up front that this suggestion is unlikely to gain approval, for reasons eloquently stated above. However, there are still some interesting issues raised that I would like to discuss. Let me first respond to a few of the comments: What's the difference between this and ``isinstance`` ? What's the difference between 'in' and 'has_key()? 1) Its shorter and more readable, 2) it can be overridden to mean different things for different container types. Your analogy doesn't apply to non dictionaries. In any case, nothing stops you from writing your own has_key() method for a different container type. Likewise, if you made an isa keyword, it would just call a method to have the traits you described above. You could write your own method to see if it was an instance of the class, but it would end up being more or less similar to isinstance(). -- http://mail.python.org/mailman/listinfo/python-list
Re: python logo
Xah Lee wrote: what's the decision? any reference to the discussion? i thought it is better for Python to have one single recognizable logo. Perhaps python doesn't have a logo and the official python people decided it shouldn't or just doesn't have one currently? of course, a logo helps in identity and as well as advertisement. Xah [EMAIL PROTECTED] ∑ http://xahlee.org/ Steve Holden wrote: Xah Lee wrote: i noticed that Python uses various logos: http://python.org/pics/pythonHi.gif http://python.org/pics/PyBanner038.gif http://python.org/pics/PyBanner037.gif http://python.org/pics/PythonPoweredSmall.gif http://wiki.python.org/pics/PyBanner057.gif is this some decision that python should use various different logos? Xah [EMAIL PROTECTED] ∑ http://xahlee.org/ Yes. -- Steve Holden +44 150 684 7255 +1 800 494 3119 Holden Web LLC http://www.holdenweb.com/ There should only be one obvious way to do it, but there are many creative ways to do it too. -- http://mail.python.org/mailman/listinfo/python-list
Re: Adding bound methods dynamically... CORRECTED
Kevin Little wrote:
I want to dynamically add or replace bound methods in a class. I want
the modifications to be immediately effective across all instances,
whether created before or after the class was modified. I need this
to work for both old ('classic') and new style classes, at both 2.3
and 2.4. I of course want to avoid side effects, and to make the
solution as light-weight as possible.
Question for the experts: Is the solution coded in AddBoundMethod()
acceptable to the Pythonian Gods? :) It does seem to work -- tested
at 2.3.5 (RH Linux) and 2.4.1 (WinXP)
[Code]
I'm not an expert, but why do you need to dynamically add or replace
bound methods?
--
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Re: aproximate a number
Thomas Bartkus wrote: On Sun, 28 Aug 2005 23:11:09 +0200, billiejoex wrote: Hi all. I'd need to aproximate a given float number into the next (int) bigger one. Because of my bad english I try to explain it with some example: 5.7 -- 6 52.987 -- 53 3.34 -- 4 2.1 -- 3 The standard way to do this is thus: def RoundToInt(x): Round the float x to the nearest integer return int(round(x+0.5)) x = 5.7 print x, '--', RoundToInt(x) x = 52.987 print x, '--', RoundToInt(x) x = 3.34 print x, '--', RoundToInt(x) x = 2.1 print x, '--', RoundToInt(x) 5.7 -- 6 52.987 -- 53 3.34 -- 4 2.1 -- 3 RoundToInt(2.0) will give you 3. -- http://mail.python.org/mailman/listinfo/python-list
Re: aproximate a number
Grant Edwards wrote: On 2005-08-30, Devan L [EMAIL PROTECTED] wrote: RoundToInt(2.0) will give you 3. That's what the OP said he wanted. The next bigger integer after 2.0 is 3. -- Grant Edwards grante Yow! I'd like TRAINED at SEALS and a CONVERTIBLE on visi.commy doorstep by NOON!! It's not really clear whether he wanted it to round up or to go to the next biggest integer because he says he has bad english. I can't think of a particular use of returning the next bigger integer. -- http://mail.python.org/mailman/listinfo/python-list
Re: Dictionary inheritance
Talin wrote:
I want to make a dictionary that acts like a class, in other words,
supports inheritance: If you attempt to find a key that isn't present,
it searches a base dictionary, which in turn searches its base, and so on.
Now, I realize its fairly trivial to code something like this using
UserDict, but given that classes and modules already have this behavior,
is there some built-in type that already does this?
(This is for doing nested symbol tables and such.)
---
Also, on a completely different subject: Has there been much discussion
about extending the use of the 'is' keyword to do type comparisons a la
C# (e.g. if x is list:) ?
-- Talin
Dictionaries aren't classes? I wasn't aware of that. Anyways, what
you're looking for, I think is a class that emulates a dictionary.
Probably you should just have some attribute that references a bigger
dictionary.
bigger_dict =
{'foo':1,'baz':2,'bar':3,'foobar':4,'foobaz':5,'foobazbar':6}
smaller_dict = {'spam':1,'ham':2,'bacon':3,'eggs':4}
smaller_dict.fallback = bigger_dict
and then the __getitem__ method might look something like
def __getitem__(self, key):
if self.has_key(key):
return self[key]
else:
return self.fallback[key]
--
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Re: Regular expression to match a #
John Machin wrote:
Aahz wrote:
In article [EMAIL PROTECTED],
John Machin [EMAIL PROTECTED] wrote:
Search for r'^something' can never be better/faster than match for
r'something', and with a dopey implementation of search [which Python's
re is NOT] it could be much worse. So please don't tell newbies to
search for r'^something'.
You're somehow getting mixed up in thinking that ^ is some kind of
not operator -- it's the start of line anchor in this context.
I can't imagine where you got that idea from.
If I change [which Python's re is NOT] to [Python's re's search() is
not dopey], does that help you?
The point was made in a context where the OP appeared to be reading a
line at a time and parsing it, and re.compile(r'something').match()
would do the job; re.compile(r'^something').search() will do the job too
-- BECAUSE ^ means start of line anchor -- but somewhat redundantly, and
very inefficiently in the failing case with dopey implementations of
search() (which apply match() at offsets 0, 1, 2, .).
I don't see much difference.
Python 2.4.1 (#65, Mar 30 2005, 09:13:57) [MSC v.1310 32 bit (Intel)]
on win32
Type copyright, credits or license() for more information.
Personal firewall software may warn about the connection IDLE
makes to its subprocess using this computer's internal loopback
interface. This connection is not visible on any external
interface and no data is sent to or received from the Internet.
IDLE 1.1.1
import timeit
t1 = timeit.Timer('re.search(^\w, will not work)','import re')
t1.timeit()
34.938577109660628
t2 = timeit.Timer('re.match(\w, will not work)','import re')
t2.timeit()
31.381461330979164
3.0/100
3.0001e-006
t1.timeit()
35.282282524734228
t2.timeit()
31.403153752781463
~4 second difference after a million times through seems to be trivial.
Then again, I haven't tested it for larger patterns and strings.
--
http://mail.python.org/mailman/listinfo/python-list
Re: Regular expression to match a #
John Machin wrote: Devan L wrote: John Machin wrote: Aahz wrote: In article [EMAIL PROTECTED], John Machin [EMAIL PROTECTED] wrote: Search for r'^something' can never be better/faster than match for r'something', and with a dopey implementation of search [which Python's re is NOT] it could be much worse. So please don't tell newbies to search for r'^something'. You're somehow getting mixed up in thinking that ^ is some kind of not operator -- it's the start of line anchor in this context. I can't imagine where you got that idea from. If I change [which Python's re is NOT] to [Python's re's search() is not dopey], does that help you? The point was made in a context where the OP appeared to be reading a line at a time and parsing it, and re.compile(r'something').match() would do the job; re.compile(r'^something').search() will do the job too -- BECAUSE ^ means start of line anchor -- but somewhat redundantly, and very inefficiently in the failing case with dopey implementations of search() (which apply match() at offsets 0, 1, 2, .). I don't see much difference. and I didn't expect that you would -- like I wrote above: Python's re's search() is not dopey. Your wording makes it hard to distinguish what exactly is dopey. -- http://mail.python.org/mailman/listinfo/python-list
Re: NEWB: General purpose list iteration?
def descend(iterable): if hasattr(iterable, '__iter__'): for element in iterable: descend(element) else: do_something(iterable) This will just do_something(object) to anything that is not an iterable. Only use it if all of your nested structures are of the same depth. If you used it on the following list of lists [[something],[[something_else],[other_thing]]] it would modify something, something_else, and other_thing. -- http://mail.python.org/mailman/listinfo/python-list
Re: Some newbie cgi form questions...
googleboy wrote: for key in form.keys():Yes, I know which fields are hidden because I made them that way, but I am trying to figure out a way I can iterate over the fields and do one thing with hidden fields (assign them to variables that tell the form how to process) and a different thing with non hidden fields (present them back to the browser with after emailling them on to the form owner). I want this script to work fro several forms on the same webserver, some of which will have several different and individual names. I am also hopeful that I may be able to extrapolate from that ways to differentiate other things from my form input things, but we'll see how it goes. My html code looks like this: h1Send Feedback/h1 form action=cgi/formparse.py method=get input name=subject type=text size=32 maxlength=196Subjectbr input name=name type=text maxlength=64Your namebr input name=email1 type=text size=24 maxlength=128Your email address. br brbrPlease let me know your thoughts below.brtextarea name=thoughts cols=64 rows=12/textareabr input type=submit value=Submit input type=hidden name=recipient value=[EMAIL PROTECTED] input type=hidden name=email value=[EMAIL PROTECTED] input type=hidden name=mailserver value=localhost input name=Clear type=button value=Clear/form In other news, I have tried suggested syntaxes aboce (thanks guys!) but I get strange errors. If the following: for key in form.keys(): if not form.keys(): print h1 ERROR! h1BR print Please go back and fill in all fields. All fields are required.br I get a traceback in teh error_log file that looks like this: Traceback (most recent call last): File cgi/form.py, line 34, in ? for key, value in form.items(): File /usr/local/lib/python2.3/cgi.py, line 533, in __getattr__ raise AttributeError, name AttributeError: items if this: for key in form.keys(): if not form.keys()[key]: print h1 ERROR! h1BR print Please go back and fill in all fields. All fields are required.br print '/body/html' the I get this traceback: Traceback (most recent call last): File /var/www/users/senta/html/gobooks/cgi/form.py, line 35, in ? if not form.keys()[key]: TypeError: list indices must be integers As you can see, I am using python 2.3 (my web service provider is responsible for this - I'd use 2.4.1 if I could) TIA googleboy import cgi form = cgi.FieldStorage() dir(form) ['FieldStorageClass', '_FieldStorage__write', '__contains__', '__doc__', '__getattr__', '__getitem__', '__init__', '__iter__', '__len__', '__module__', '__repr__', 'bufsize', 'disposition', 'disposition_options', 'done', 'file', 'filename', 'fp', 'getfirst', 'getlist', 'getvalue', 'has_key', 'headers', 'innerboundary', 'keep_blank_values', 'keys', 'length', 'list', 'make_file', 'name', 'outerboundary', 'read_binary', 'read_lines', 'read_lines_to_eof', 'read_lines_to_outerboundary', 'read_multi', 'read_single', 'read_urlencoded', 'skip_lines', 'strict_parsing', 'type', 'type_options'] The form is not a dictionary. -- http://mail.python.org/mailman/listinfo/python-list
Re: Fat and happy Pythonistas (was Re: Replacement for keyword 'global' good idea? ...)
advisedly) against the map, filter and reduce operators? It seems to be completely irrational from my viewpoint. I've seen the arguements, and they make no sense. Map and filter are not special. Why have two ways to do the same thing? Reduce is a special case, but the arguments against map and filter are quite sensible. BTW, I think large and stable would have been less offensive than fat and happy, but perhaps you meant to imply we're both lazy and complacent, rather than just satisfied with something that works and not inclined to shoot for moving targets every working day. If so, I'm not sure why you'd say that, since the evidence doesn't support it. I'm not suggesting shooting at a moving target. I'm suggesting getting the head out of the sand, looking at trends, and figuring out the _large_ steps to take next, not the nickle and dime fixups that are the only things I see in PEP 3000. (Not to say that some of them aren't going to be a lot of work. Some of them are.) I came back from Agile2005 last week. The open space session on Ruby was maybe 5 times as large as the one on Python. And both of them were kind of an afterthought. Look at the OSCon blogs. There were a number of hardcore Python people there. They couldn't get into Ruby sessions because they were jammed. Standing room only. More people does not mean better. There's a report out that the scripting languages in general are losing mindshare big time in Europe, Africa and the east in general. In fact, everywhere except in North America. I'm generally somewhat skeptical of these reports unless I can see the methodology, but it's definitely a data point. Another thing that stands out: the explicit versus dynamic typing debate has moved on from program correctness (which is a wash) to other areas that explicit (or derived) type information can be used for. I see this in PyFit: the languages where explicit type information is available by reflection have cleaner implementations. The languages with dynamic typing all have to deal with the fact that they can't get type information by reflection, and it's a diverse mess. The world is moving on, in ways that I think you're not seeing. And Python is standing still in many of those same ways. Take another look then. -Devan L -- http://mail.python.org/mailman/listinfo/python-list
Re: Newbie Program
Eric wrote: I am reading a book on Python and ran across and exercise that I just can't seem to figure out. Its pretty simple, but I just can't get past a certain point. The task is to create a program that flips a coin 100 times and keeps track of the total of heads and tails which is printed to the screen. My plan was to use import random with a range of 2 and use a conditional statement to count to 100. The problem I am encountering is how do I keep track of the totals for heads and tails? Any suggestions would be appreciated. Keep in mind I am very new to Python so there may be a more sophisticated way, but I am just trying to use what the book has taught so far. Thanks, Eric Someone else read the same book, I suppose. http://groups-beta.google.com/group/comp.lang.python/browse_thread/thread/87fcaf8ffbbd69e7/c7ff2d2b5b0d776d?q=coin+fliprnum=3#c7ff2d2b5b0d776d -- http://mail.python.org/mailman/listinfo/python-list
Re: Wheel-reinvention with Python
Ed Leafe wrote: On Sunday 31 July 2005 22:39, Paul Rubin wrote: import dabo app = dabo.dApp() dApp.start() Sorry, I couldn't do it in 5. ;-) Oh, and that includes a full menu, too. I get an ImportError exception when I try that. Any suggestions? Note that I don't get that exception from Tkinter. bash-3.00$ python Python 2.3.4 (#1, Oct 26 2004, 16:42:40) [GCC 3.4.2 20041017 (Red Hat 3.4.2-6.fc3)] on linux2 Type help, copyright, credits or license for more information. import dabo Traceback (most recent call last): File stdin, line 1, in ? ImportError: No module named dabo import Tkinter Oh, c'mon now Paul, now you're trolling. You know exactly what the problem is, and try to make it look like a bug. Fine: you don't want to use anything that doesn't come standard with Python. You've made your point. We get it. There is no need to repeat yourself constantly. The only point of my post was that for those without your aversion to installing useful tools, Dabo provides a ton of functionality. Also, as my partner Paul McNett pointed out, I could have done it in *two* lines: import dabo dabo.dApp().start() ;-) -- -- Ed Leafe -- http://leafe.com -- http://dabodev.com If you're creating a new instance of your dApp(I assume its a class) with no arguments, then effectively your just creating a default program which is already defined in the dabo module. If you could write it in a few, short lines of code by defining a new class, then you might have something there. -- http://mail.python.org/mailman/listinfo/python-list
Re: [pygame]how to copy a surface to an other surface with alpha value?
flyaflya wrote: I want to join some surfaces to a new big surface with alpha cannel, I want the new surface has same pixels(inclue r,g,b and alpha value) as the pixels on the source surfaces. my code as follow: surf = pygame.Surface((200,200)) surf.blit(surf1, (0,0)) surf.blit(surf2, (0,100)) . but these codes can't copy alpha value to the new surface.how can I deal with it? Try the pygame mailing list or irc channel. http://www.pygame.org/info.shtml -- http://mail.python.org/mailman/listinfo/python-list
Re: searching string url
Sounds somewhat like homework. So I won't just give you a code solution. Use the regular expression(re) module to match the urls. -- http://mail.python.org/mailman/listinfo/python-list
Re: A Module on Time Date
Robert Maas, see http://tinyurl.com/uh3t wrote: From: Robert Kern [EMAIL PROTECTED] As you can see in the datetime documentation, the module was introduced in Python 2.3. I recommend updating your Python installation. What do you mean your?? I don't have any Python installation of my own. All I have is what this small local ISP provides on its Unix shell machine which I share with hundreds of other users. There's no way I can install a new version of anything on the system account. Your recommendation will be disregarded as total crap. plonk You should contact your isp and ask them to upgrade, then. -- http://mail.python.org/mailman/listinfo/python-list
Re: Problem loading a file of words
teoryn wrote:
I've been spending today learning python and as an exercise I've ported
a program I wrote in java that unscrambles a word. Before describing
the problem, here's the code:
*--beginning of file--*
#!/usr/bin/python
# Filename: unscram.py
def sort_string(word):
'''Returns word in lowercase sorted alphabetically'''
word = str.lower(word)
word_list = []
for char in word:
word_list.append(char)
word_list.sort()
sorted_word = ''
for char in word_list:
sorted_word += char
return sorted_word
print 'Building dictionary...',
dictionary = { }
# Notice that you need to have a file named 'dictionary.txt'
# in the same directory as this file. The format is to have
# one word per line, such as the following (of course without
# the # marks):
#test
#hello
#quit
#night
#pear
#pare
f = file('dictionary.txt')
# This loop builds the dictionary, where the key is
# the string after calling sort_string(), and the value
# is the list of all 'regular' words (from the dictionary,
# not sorted) that passing to sort_string() returns the key
while True:
line = f.readline()
if len(line) == 0:
break
line = str.lower(line[:-1]) # convert to lowercase just in case
and
# remove the return at the end of
the line
sline = sort_string(line)
if sline in dictionary: # this key already exist, add to
existing list
dictionary[sline].append(line)
print 'Added %s to key %s' % (line,sline) #for testing
else: # create new key and list
dictionary[sline] = [line]
print 'Created key %s for %s' % (sline,line) #for
testing
f.close()
print 'Ready!'
# This loop lets the user input a scrambled word, look for it in
# dictionary, and print all matching unscrambled words.
# If the user types 'quit' then the program ends.
while True:
lookup = raw_input('Enter a scrambled word : ')
results = dictionary[sort_string(lookup)]
for x in results:
print x,
print
if lookup == 'quit':
break
*--end of file--*
If you create dictionary.txt as suggested in the comments, it should
work fine (assumeing you pass a word that creates a valid key, I'll
have to add exceptions later). The problem is when using a large
dictionary.txt file (2.9 MB is the size of the dictionary I tested) it
always gives an error, specifically:
(Note: ccehimnostyz is for zymotechnics, which is in the large
dictionary)
*--beginning of example--*
Enter a scrambled word : ccehimnostyz
Traceback (most recent call last):
File unscram.py, line 62, in ?
results = dictionary[sort_string(lookup)]
KeyError: 'ccehimnostyz'
*--end of example--*
If you'd like a copy of the dictionary I'm using email me at teoryn at
gmail dot com or leave your email here and I'll send it to you (It's
702.2 KB compressed)
Thanks,
Kevin
Heh, it reminds me of the code I used to write.
def sort_string(word):
return ''.join(sorted(list(word.lower(
f = open('dictionary.txt','r')
lines = [line.rstrip('\n') for line in f.readlines()]
f.close()
dictionary = dict((sort_string(line),line) for line in lines)
lookup = ''
while lookup != 'quit':
lookup = raw_input('Enter a scrambled word:')
if dictionary.has_key(lookup):
word = dictionary[lookup]
else:
word = 'Not found.'
print word
You need python 2.4 to use this example.
--
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Re: Problem loading a file of words
Robert Kern wrote: That's definitely not the kind of dictionary that he wants. -- Robert Kern [EMAIL PROTECTED] In the fields of hell where the grass grows high Are the graves of dreams allowed to die. -- Richard Harter Oh, I missed the part where he put values in a list. -- http://mail.python.org/mailman/listinfo/python-list
Re: Odd behaviour of regexp module
Why doesn't group have an argument? group() or group(0) returns what the pattern matched, not what it returns. -- http://mail.python.org/mailman/listinfo/python-list
Re: question on input
Use raw_input instead. It returns a string of whatever was typed. Input expects a valid python expression. -- http://mail.python.org/mailman/listinfo/python-list
Re: Help with inverted dictionary
import re
name = Robert
f = file('phonebook.txt','r')
lines = [line.rstrip(\n) for line in f.readlines()]
pat = re.compile(name, re.I)
related_lines = [line for line in lines if pat.search(line)]
And then you write the lines in related_lines to a file. I don't really
write text to files much so, um, yeah.
--
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Re: Creating anonymous functions using eval
How is this different from a nested function? -- http://mail.python.org/mailman/listinfo/python-list
Re: Help with inverted dictionary
I think you need to get a database. Anyways, if anything, it should create no more than 5,000 files, since 5,000 facts shouldn't talk about 30,000 animals. There have been a few discussions about looking at files in directories though, if you want to look at those. -- http://mail.python.org/mailman/listinfo/python-list
Re: Help with inverted dictionary
Oh, I seem to have missed the part saying 'or other word'. Are you doing this for every single word in the file? -- http://mail.python.org/mailman/listinfo/python-list
Re: Creating anonymous functions using eval
Well, the string that gets passed is more or less a function definition, which is then called with exec. I don't see why you'd need to write a string out with the function definition and then call it. You could just write the function. As for the nested functions, I had been presuming that it was intended to use as a better function than lambda within a function. Sorry for the confusion. -- http://mail.python.org/mailman/listinfo/python-list
Re: automatically assigning names to indexes
import math class Vector: def __init__(self, coordinates): self.coordinates = coordinates self.magnitude = sum([c**2 for c in coordinates])**0.5 self.direction = getangle(Vector([1]+[0 for i in range(len(coordinates)-1)])) def dotproduct(self, vector): sum([a*b for a,b in zip(self.coordinates,vector.coordinates)]) def crossproduct(self, vector, pvector): return pvector*self.magnitude*vector.magnitude*math.sin(self.getangle(vector)) def getangle(self, vector): return math.acos(self.dotproduct(vector)/(self.magnitude*vector.magnitude)) def __mul__(self, scalar): return Vector([c*scalar for c in self.coordinates]) def __add__(self, vector): return Vector([c+d for c,d in zip(self.coordinates,vector.coordinates)]) def __sub__(self, vector): return Vector([c-d for c,d in zip(self.coordinates,vector.coordinates)]) What about this? -- http://mail.python.org/mailman/listinfo/python-list
Re: Creating anonymous functions using eval
You missed Steven's point which is to quote the message to which you are replying. Not everyone is reading this list in a conveniently threaded form, so you need to provide some context for them to be able to follow along. Ah, sorry, I didn't quite get what he was referring to. -- http://mail.python.org/mailman/listinfo/python-list
Re: Yet Another Python Web Programming Question
Take some time to learn one of the web frameworks. If your host doesn't already have it, ask your host if they would consider adding it. -- http://mail.python.org/mailman/listinfo/python-list
Re: Python Forum
I see a total of 12 posts and 8 users. -- http://mail.python.org/mailman/listinfo/python-list
Re: removing list comprehensions in Python 3.0
List comprehensions are faster than generator comprehensions for iterating over smaller sequences. -- http://mail.python.org/mailman/listinfo/python-list
Re: removing list comprehensions in Python 3.0
import timeit
t1 = timeit.Timer('list(i for i in xrange(10))')
t1.timeit()
27.267753024476576
t2 = timeit.Timer('[i for i in xrange(10)]')
t2.timeit()
15.050426800054197
t3 = timeit.Timer('list(i for i in xrange(100))')
t3.timeit()
117.61078097914682
t4 = timeit.Timer('[i for i in xrange(100)]')
t4.timeit()
83.502424470149151
Hrm, okay, so generators are generally faster for iteration, but not
for making lists(for small sequences), so list comprehensions stay.
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Re: map/filter/reduce/lambda opinions and background unscientific mini-survey
Here's a couple of examples from my own code:
# from a Banzhaf Power Index calculator
# adds things that aren't numbers
return reduce(operator.add,
(VoteDistributionTable({0: 1, v: 1}) for v in electoral_votes))
return sum([VoteDistributionTable({0:1, v:1} for v in
electoral_votes],VoteDistributionTable({}))
Any time you use operator.add, you can probably use
sum(sequence,initialvalue)
# from a custom numeric class
# converts a tuple of digits into a number
mantissa = sign * reduce(lambda a, b: 10 * a + b, mantissa)
I'll admit I can't figure out a way to replace reduce without writing
some ugly code here, but I doubt these sorts of things appear often.
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Re: map/filter/reduce/lambda opinions and background unscientific mini-survey
def flatten(iterable): if not hasattr(iterable, '__iter__'): return [iterable] return sum([flatten(element) for element in iterable],[]) Recursion makes things so much shorter. -- http://mail.python.org/mailman/listinfo/python-list
Re: Favorite non-python language trick?
Okay, maybe that was too restrictive, reduce can *usually* be replaced with sum. Sorry about that. -- http://mail.python.org/mailman/listinfo/python-list
Re: map/filter/reduce/lambda opinions and background unscientific mini-survey
Claiming that sum etc. do the same job is the whimper of someone who doesn't want to openly disagree with Guido. Could you give an example where sum cannot do the job(besides the previously mentioned product situation? Also, map is easily replaced. map(f1, sequence) == [f1(element) for element in sequence] -- http://mail.python.org/mailman/listinfo/python-list
Re: Favorite non-python language trick?
sum(sequence[0] + [1/element for element in sequence[1:]]) I think that should work. -- http://mail.python.org/mailman/listinfo/python-list
Re: Regular Expression for pattern substitution
re.replace. I don't think there's any way to avoid it. Except maybe having an alias email address or a fake one. -- http://mail.python.org/mailman/listinfo/python-list
Re: map/filter/reduce/lambda opinions and background unscientific mini-survey
None of them are really indispensible. Map and filter cab be replaced with list comprehensions. reduce is redundant except when multiplying a series; there's a sum function for a reason. Lambda looks cleaner in some cases, but you don't gain any functionality. What really struck me, though, is the last line of the abstract: I expect tons of disagreement in the feedback, all from ex-Lisp-or-Scheme folks. :-) Guido wrote somewhere that the original map, filter, and reduce came from a lisp hacker who missed them. -- http://mail.python.org/mailman/listinfo/python-list
Re: Regular Expression for pattern substitution
Hrm, thought it had one. Guess it would help if I actually used regular expression for replacement. -- http://mail.python.org/mailman/listinfo/python-list
Re: class attribute to instance attribute
Well, I've never heard of a method like that for assigning variables. I'd rather put it in the __init__ method. -- http://mail.python.org/mailman/listinfo/python-list
Re: Favorite non-python language trick?
With the exception of reduce(lambda x,y:x*y, sequence), reduce can be replaced with sum, and Guido wants to add a product function. -- http://mail.python.org/mailman/listinfo/python-list
Re: Python for everything?
Python for everything except things that need to be ridiculously optimized for speed. Thats what C embedded in Python and Psyco enhanced Python code is for. Oh wait, thats still all Python... -- http://mail.python.org/mailman/listinfo/python-list
Re: class attribute to instance attribute
Why make it an instance attribute? Couldn't you just look at the class attribute? If its something that depends on each instance's value assigned to the attribute, why not make it an instance attribute to start with? -- http://mail.python.org/mailman/listinfo/python-list
Re: How to run commands in command line from a script
The code module, perhaps? http://www.python.org/doc/2.4.1/lib/module-code.html -- http://mail.python.org/mailman/listinfo/python-list
Re: Escaping commas within parens in CSV parsing?
Try this. re.findall(r'(.+? \(.+?\))(?:,|$)',yourtexthere) -- http://mail.python.org/mailman/listinfo/python-list
Re: Splitting string into dictionary
One line solution. dict(re.findall(r'(.+?)' \| '(.+?)'(?:\s\||$),yourtexthere)) -- http://mail.python.org/mailman/listinfo/python-list
Re: regulars expressions ?
re.findall(r'?(.+?)?(?:,|$)', yourtexthere) -- http://mail.python.org/mailman/listinfo/python-list
Re: regulars expressions ?
Oh, oops, sorry, that code doesn't respect the quotes. Use this code: re.findall(r'(.+?|\S+)(?:,|$)', yourtexthere) -- http://mail.python.org/mailman/listinfo/python-list
Re: Newbie: Help Figger Out My Problem
import random flips = 100 results = [random.randint(0,1) for i in range(flips)] heads = results.count(0) tails = results.count(1) print Heads:%s % heads print Tails:%s % tails I think this is more compact. -- http://mail.python.org/mailman/listinfo/python-list
Re: When someone from Britain speaks, Americans hear a British accent...
Thats like posting about Google here because the newsgroup is hosted on Google. -- http://mail.python.org/mailman/listinfo/python-list
Re: noob question
To recognize variables that you have assigned, just look for assignment. If your code is readible, and you know it well, you shouldn't need the $ sign in front of everything. -- http://mail.python.org/mailman/listinfo/python-list
Re: Favorite non-python language trick?
return a if a.value == true database.query(q) unless database.connect == error (etc) if a.value == True: return a if not database.connect == error: database.query(q) Trading two words for one word doesn't necessarily make the code better. unless false then print 1 # this prints 1 forever while not False: print 1 unless seems to become while not, as opposed to if not. Should be more consistent. -- http://mail.python.org/mailman/listinfo/python-list
Re: Favorite non-python language trick?
Why overload when you can use class methods? -- http://mail.python.org/mailman/listinfo/python-list
Re: what list comprehension can't
I wasn't aware that python supported if then else. -- http://mail.python.org/mailman/listinfo/python-list
