Re: def X(l=[]): weirdness. Python bug ?
Bart van Deenen wrote: Hi all. I've stumbled onto a python behavior that I don't understand at all. Python 2.5.2 (r252:60911, Jul 31 2008, 17:28:52) # function def X(l=[]): l.append(1) print l # first call of X X() [1] #second call of X X() [1, 1] Where does the list parameter 'l' live between the two successive calls of X(). Why is it not recreated with an empty list? Is this correct behavior or is it a Python bug? Does anyone have any pointers to the language documentation where this behavior is described? Thanks all Bart van Deenen I happen to be reading about decorators at the moment: from copy import deepcopy def nodefault(myfunc): myfunc_defaults = myfunc.func_defaults def fresh(*args, **kwargs): myfunc.func_defaults = deepcopy(myfunc_defaults) return myfunc(*args, **kwargs) return fresh @nodefault def X(l=[]): l.append(1) print l for i in range(1,6): ... X() ... [1] [1] [1] [1] [1] Which is just a very fancy way of doing: def X(l=[]): if l is None: l = [] l.append(1) print l * sound of two pennies * -- http://mail.python.org/mailman/listinfo/python-list
Re: Write bits in file
Tim Roberts wrote: Monica Leko [EMAIL PROTECTED] wrote: I have a specific format and I need binary representation. Does Python have some built-in function which will, for instance, represent number 15 in exactly 10 bits? For the record, I'd like to point out that even C cannot do this. You need to use shifting and masking to produce a stream of 8-bit bytes, or to extract your values from a stream of 8-bit bytes. H, bitfields are exactly non-aligned bits in a structure and are part of ANSI C. Although C gives no guarantee of the ordering of fields within machine words ... so bitfieds are of limited use in portable programs unless they are 0-initialized. IIRC, Huffman code uses arbitrary length bit strings and is the basis of many compression algorithms. -- http://mail.python.org/mailman/listinfo/python-list
Re: can python do some kernel stuff?
Jimmy wrote: Hi to all python now has grown to a versatile language that can accomplish tasks for many different purposes. However, AFAIK, little is known about its ability of kernel coding. So I am wondering if python can do some kernel coding that used to be the private garden of C/C++. For example, can python intercept the input of keyboard on a system level? someone told me it's a kernel thing, isn't it? http://wiki.python.org/moin/elmer -- http://mail.python.org/mailman/listinfo/python-list
Re: [Regexes] Stripping puctuation from a text
shabda raaj wrote:
I want to strip punctuation from text.
So I am trying,
p = re.compile('[a-zA-Z0-9]+')
p.sub('', 'I love tomatoes!! hell yeah! ... Why?')
' !! ! ... ?'
Which gave me all the chars which I want to replace.
So Next I tried by negating the regex,
p = re.compile('^[a-zA-Z0-9]+')
p.sub('', 'I love tomatoes!! hell yeah! ... Why?')
' love tomatoes!! hell yeah! ... Why?'
But this removed the first char instead of the puctuation. So I guess
^ is matching start of line, instead of negation. How can I take
negation of the regex here?
p = re.compile('[^a-zA-Z0-9]+')
--
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Re: php vs python
notbob wrote: I'm not posting this just to initiate some religious flame war, though it's the perfect subject to do so. No, I actaully want some serious advice about these two languages and since I think usenet is the best arena to find it, here ya' go. So, here's my delimna: I want to start a blog. Yeah, who doesn't. Yet, I want learn the guts of it instead of just booting up some wordwank or whatever. I started to learn python, but heard php was easier or faster or more like shell scripting or... fill in the blank. Anyway, so I change over to learning php. Then I run across that blog, Coding Horror, and start reading articles like this: http://www.codinghorror.com/blog/archives/001119.html Now what? Go back to python. Soldier on with php? What do I know? Not much. I can setup mysql and apache,, but don't know how to use 'em, really. I use emacs and run slackware and can fumble my way through bash scripts, but I can't really write them or do lisp. I've taken basic basic and basic C, but am barely literate in html. Sometimes it seems overwhelming, but I persevere because it's more fun/challenging than video games, which bore me to tears. Well, that's my actual question, then. Is php really so bad I'm just wasting my time? Or is it really the quickest way to blog functionality? Would I be better served in the long run learning python, which claims to be easy as pie to learn/program (still looks hard to me). I admit I'm no code geek. But, I'm not completely brain dead, either, and I need something to keep my geezer brain sparking. What say ye? nb Personally, I believe PHP would get you more productive more quickly for a blog, but it is a potentially brain damaging language in terms of really getting your juices flowing with programming. It is not a general purpose language and suffers from all the limitations of of a tool designed for one job. If you are interested in programming and the blog is your path to that, stick with Python! In particular, immerse yourself in mod_python or look at a framework like Django or Pylons -- the learning curve is steep for any of these technologies but they are a full meal compared to saltine cracker and water of PHP. -- http://mail.python.org/mailman/listinfo/python-list
Re: can python do some kernel stuff?
Jimmy wrote: On May 23, 3:05 pm, Andrew Lee [EMAIL PROTECTED] wrote: Jimmy wrote: Hi to all python now has grown to a versatile language that can accomplish tasks for many different purposes. However, AFAIK, little is known about its ability of kernel coding. So I am wondering if python can do some kernel coding that used to be the private garden of C/C++. For example, can python intercept the input of keyboard on a system level? someone told me it's a kernel thing, isn't it? http://wiki.python.org/moin/elmer well, straightly speaking, how can I know a key is pressed on a system- level if using python? http://docs.python.org/lib/module-curses.html Unless you are using an ancient piece of hardware -- a terminal is a pseudo terminal and a key stroke isn't a kernel event at all. If you were looking for examples of kernel level functions you might want to consider driver interfaces -- how to program device interfaces -- that, too, can be done in Python -- but, again, you are always calling some underlying C function exposed via SWIG or another cross compilation tool. Python doesn't reinvent system calls! :-) -- http://mail.python.org/mailman/listinfo/python-list
Re: can python do some kernel stuff?
Diez B. Roggisch wrote: Jimmy schrieb: On May 23, 3:05 pm, Andrew Lee [EMAIL PROTECTED] wrote: Jimmy wrote: Hi to all python now has grown to a versatile language that can accomplish tasks for many different purposes. However, AFAIK, little is known about its ability of kernel coding. So I am wondering if python can do some kernel coding that used to be the private garden of C/C++. For example, can python intercept the input of keyboard on a system level? someone told me it's a kernel thing, isn't it? http://wiki.python.org/moin/elmer well, straightly speaking, how can I know a key is pressed on a system- level if using python? What has that todo with kernel programming? You can use e.g. pygame to get keystrokes. Or under linux, read (if you are root) the keyboard input file - I've done that to support several keyboards attached to a machine. And the original question: no, python can't be used as kernel programming language. Amongst other reasons, performance the GIL prevent that. Diez http://www.kernel-panic.it/programming/py-pf/ Of course you can code kernel routines in Python -- you are just calling the underlying C interface. The GIL means you have to manage threadsafety on your own -- it doesn't imply kernel programming can not be done. I'm not talking about writing an OS in Python (though a simple DOS-like OS is very possible). Nor would I suggest writing device drivers in Python -- but of course you can call kernel routines and manage some kernel resources effectively. Python's IPC libraries expose kernel functionality. -- http://mail.python.org/mailman/listinfo/python-list
Re: can python do some kernel stuff?
Diez B. Roggisch wrote: Andrew Lee schrieb: Diez B. Roggisch wrote: Jimmy schrieb: On May 23, 3:05 pm, Andrew Lee [EMAIL PROTECTED] wrote: Jimmy wrote: Hi to all python now has grown to a versatile language that can accomplish tasks for many different purposes. However, AFAIK, little is known about its ability of kernel coding. So I am wondering if python can do some kernel coding that used to be the private garden of C/C++. For example, can python intercept the input of keyboard on a system level? someone told me it's a kernel thing, isn't it? http://wiki.python.org/moin/elmer well, straightly speaking, how can I know a key is pressed on a system- level if using python? What has that todo with kernel programming? You can use e.g. pygame to get keystrokes. Or under linux, read (if you are root) the keyboard input file - I've done that to support several keyboards attached to a machine. And the original question: no, python can't be used as kernel programming language. Amongst other reasons, performance the GIL prevent that. Diez http://www.kernel-panic.it/programming/py-pf/ Of course you can code kernel routines in Python -- you are just calling the underlying C interface. The GIL means you have to manage threadsafety on your own -- it doesn't imply kernel programming can not be done. I understood the OP's question as can one program kernelspace routines in python. Which I don't think is possible. And I don't see how py-pf does that either. Diez OP: I am wondering if python can do some kernel coding that used to be the private garden of C/C++. The answer is yes. IPC and py-pf are examples. If you don't think of packet filtering as kernel coding, I can understand. But clearly the Python interfaces to fork(), waitpid(), signal(), alarm() and so forth are forays into the once private garden of C. -- http://mail.python.org/mailman/listinfo/python-list
Re: Markov Analysis Help
dave wrote:
Hi Guys,
I've written a Markov analysis program and would like to get your
comments on the code As it stands now the final input comes out as a
tuple, then list, then tuple. Something like ('the', 'water') ['us']
('we', 'took')..etc...
I'm still learning so I don't know any advanced techniques or methods
that may have made this easier.
here's the code:
def makelist(f): #turn a document into a list
fin = open(f)
results = []
for line in fin:
line = line.replace('', '')
line = line.strip().split()
for word in line:
results.append(word)
return results
What's you data look like? Just straight text?
def markov(f, preflen=2):#f is the file to analyze, preflen is
prefix length
convert_file = makelist(f)
mapdict = {}#dict where the prefixes will map to suffixes
start = 0
end = preflen #start/end set the slice size
for words in convert_file:
prefix = tuple(convert_file[start:end]) #tuple as mapdict key
suffix = convert_file[start + 2 : end + 1] #word as suffix to key
mapdict[prefix] = mapdict.get(prefix, []) + suffix #append suffixes
start += 1
end += 1
return mapdict
What is convert_file??
def randsent(f, amt=10): #prints a random sentence
analyze = markov(f)
for i in range(amt):
rkey = random.choice(analyze.keys())
print rkey, analyze[rkey],
The book gave a hint saying to make the prefixes in the dict using:
def shift(prefix, word):
return prefix[1:] + (word, )
That's not a very helpful hint.
It works if you call it with a tuple and a word --- it shifts off the
front of the tuple ... so :
shift(('foo','bar') word)
becomes ('bar', 'word')
Whoopty doo --- I'm not sure what that accomplishes!!
Unless the author means pass a list and a randomly pick a word from the
list in which case the return statement could be
random.choice(prefix) + (word, )
* shrug *
But -- that's not very Markov ... you'd want a weighted choice of words
... depending on how you define your Markov chain -- say a Markov chain
based on part-of-speech or probability of occurrence from a given word-set.
Can you give some more detail??
However I can't seem to wrap my head around incorporating that into the
code above, if you know a method or could point me in the right
direction (or think that I don't need to use it) please let me know.
Thanks for all your help,
Dave
--
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Re: Python is slow
cm_gui wrote: Python is slow.Almost all of the web applications written in Python are slow. Zope/Plone is slow, sloow, so very slooow. Even Google Apps is not faster. Neither is Youtube. Facebook and Wikipedia (Mediawiki), written in PHP, are so much faster than Python. Okay, they probably use caching or some code compilation -- but Google Apps and those Zope sites probably also use caching. I've yet to see a web application written in Python which is really fast. So --- don't use Google * shrug * Personally I find PHP to be a hideous language -- it has only one use. It is Perl for people who can be bothered to learn a general purpose programming language and just write web applications. Python is a general purpose programming language ... it does web nicely (Django and pylons!), it supports real OOP and OOD, it's extensible, it has a smart set of libraries, intelligent and coherent interfaces, it sails across platforms, it has at least one great ORM (SQLAlchemy) and I keep discovering new cool things about the language as a recent convert that make me wonder why I would ever write another large application in Perl or Java. I find Zope to be a mess and it gives me a headache ... but it Zope is an *application framework*, not a *programming language*. So, I think you are barking up the wrong straw man (if I may mix metaphors). But that's just my $0.02. -- http://mail.python.org/mailman/listinfo/python-list
Re: Why is math.pi slightly wrong?
Mensanator wrote: On May 22, 11:32 am, Dutton, Sam [EMAIL PROTECTED] wrote: I've noticed that the value of math.pi -- just entering it at the interactive prompt -- is returned as 3.1415926535897931, whereas (as every pi-obsessive knows) the value is 3.1415926535897932... (Note the 2 at the end.) Is this a precision issue, or from the underlying C, or something else? How is math.pi calculated? If you actually need that many digits, use a different library. import gmpy print gmpy.pi(64) # 64 bit precision 3.14159265358979323846 print gmpy.pi(128) # 128 bit precision 3.141592653589793238462643383279502884197 print gmpy.pi(16384) # 16384 bit precision 3.14159265358979323846264338327950288419716939937510582097494459 23 Heh! I wonder who needs that many digits? Certainly not number theorists (they need a LOT more). Certainly not physicists -- they need about 30 digits to be within 1% of any measurement from molecules to galaxies. Certainly not engineers, they need half the digits that physicists need. Cryptographers are making a dire mistake if they are using PI in any computations (possible exception for elliptic curves -- see number theorists, above) ... so -- other than PI-philes, who needs PI to thousands of digits? -- http://mail.python.org/mailman/listinfo/python-list
Re: Why is math.pi slightly wrong?
Dan Upton wrote: On Thu, May 22, 2008 at 2:53 PM, Mensanator [EMAIL PROTECTED] wrote: On May 22, 11:32 am, Dutton, Sam [EMAIL PROTECTED] wrote: I've noticed that the value of math.pi -- just entering it at the interactive prompt -- is returned as 3.1415926535897931, whereas (as every pi-obsessive knows) the value is 3.1415926535897932... (Note the 2 at the end.) Is this a precision issue, or from the underlying C, or something else? How is math.pi calculated? If you actually need that many digits, use a different library. import gmpy print gmpy.pi(64) # 64 bit precision 3.14159265358979323846 print gmpy.pi(128) # 128 bit precision 3.141592653589793238462643383279502884197 print gmpy.pi(16384) # 16384 bit precision 3.14159265358979323846264338327950288419716939937510582097494459 ... Who wants to verify that that's correct to that many digits? ;) Ramanujan? http://numbers.computation.free.fr/Constants/Pi/piramanujan.html -- http://mail.python.org/mailman/listinfo/python-list
Re: MVC
George Maggessy wrote: Hi Gurus, I'm a Java developer and I'm trying to shift my mindset to start programming python. So, my first exercise is to build a website. However I'm always falling back into MVC pattern. I know it's a standard, but the implementation language affects the use of design patter. So, here goes my question. Is that OK if I follow this? Should I create DAOs, View Objects, Controllers and etc? Is there any sort of best practice / standard to Python? Cheers, George Look at Pylons. -- http://mail.python.org/mailman/listinfo/python-list
Re: MatplotLib errors
Thomas Philips wrote: I have just started using MatPlotLib, and use it to generate graphs from Python simulations. It often happens that the graph is generated and a Visual C++ Runtime Library error then pops up: Runtime Error! Program C:\Pythin25\Pythonw.exe This application has requested the Runtime to terminate in an unusual way. Please contact the application's support team for more information. I'm running Python 2.5.2 under Windows XP. Any thoughts on what what may be causing the problem? Thanks in advance Thomas Philips There is a matplotlib-sig mailing list: [EMAIL PROTECTED] They would have MUCH more info on your problem that can be offered in a general python group. HTH -- http://mail.python.org/mailman/listinfo/python-list
Re: help needed with classes/inheritance
barbaros wrote: Hello everybody, I am building a code for surface meshes (triangulations for instance). I need to implement Body objects (bodies can be points, segments, triangles and so on), then a Mesh will be a collection of bodies, together with their neighbourhood relations. I also need OrientedBody objects, which consist in a body together with a plus or minus sign to describe its orientation. So, basically an OrientedBody is just a Body with an integer label stuck on it. I implemented it in a very crude manner: -- class Body: [...] class OrientedBody: def __init__ (self,b,orient=1): # b is an already existing body assert isinstance(b,Body) self.base = b self.orientation = orient --- class Body(object) : ... class OrientedBody (Body): def __init__(self, orientation = 1) : Body.__init__(self) self.orientation = orientation as noted But, also. as a rule of thumb .. if you are using isinstance in a class to determine what class a parameter is ... you have broken the OO contract. Remember, every class ought to have a well defined internal state and a well defined interface to its state. If I write -- class foo (object): def __init__ : pass def some_func (self, val) : if isinstance (val, bar) : Then I am either doing something very wrong or very clever (either can get me in trouble) In Python it is preferred that I write two functions some_func_a and some_func_b e.g. def some_func_a (self, val = None, class = bar) : assert(isinstance (class, bar), True) def some_func_b (self, val = None, class = baz) : assert (isinstance (class, baz), True) C++ and Java try to enforce the OO contract by making data and methods private, protected or public. Which helps -- but leads to some confusion (what is protected inheritance in C++) Python exposes all of its classes internals to everyone -- but that doesn't mean you should touch them!! As Larry Wall once wrote, There is a difference between, 'do not enter my living room because I asked you not to' and 'do not enter my living room because I have a shotgun' Python adopts the 'do not touch my private parts because I asked you not to' idiom. (In C++, only friends can touch your privates ... ;-) So -- be mindful that checking the class of well defined parameters at anytime is breaking the contract -- you may need to do it -- but it is more likely that you aren't adhering to good OOD. Does that make any sense? Seriously -- I have not had any coffee yet and I am still new at Python. -- Andrew My question is: can it be done using inheritance ? I recall that I need three distinct objects: the basic (non-oriented) body, the same body with positive orientation and the same body with negative orientation. Thank you. Cristian Barbarosie http://cmaf.fc.ul.pt/~barbaros -- http://mail.python.org/mailman/listinfo/python-list
Re: Checking if a text file is blank
[EMAIL PROTECTED] wrote: Greetings! I've just started learning python, so this is probably one of those obvious questions newbies ask. Is there any way in python to check if a text file is blank? What I've tried to do so far is: f = file(friends.txt, w) if f.read() is True: do stuff else: do other stuff f.close() What I *mean* to do in the second line is to check if the text file is not-blank. But apparently that's not the way to do it. Could someone set me straight please? Along with the other posts ... consider using the lstat command to get information about the file. import os print os.lstat(friends.txt)[6] gives the size in bytes of friends.txt or throws an OSError if friends.txt does not exist. lstat is portable, it defaults to stat on Windows. -- http://mail.python.org/mailman/listinfo/python-list
Re: Checking if a text file is blank
David wrote: import os print os.lstat(friends.txt)[6] I prefer os.lstat(friends.txt).st_size MUCH easier to remember Thanks! -- http://mail.python.org/mailman/listinfo/python-list
Announce : TimeDuration 0.1a released
This is a pure python module for parsing time interval strings, normalizing, comparing and ordering time intervals. This module is still in alpha phase. It handles string like : 1 hour, 15 minutes and 23.2 seconds 01:15:23.2 1h 15min 23.2sec Output from *nix uptime or time commands : 15 days, 23:04 0m2.496s It handles comparisons and sorting of TimeDuration objects. It normalizes time interval strings, e.g. : 5 d, 27 h, 75 m 120 s will normalize to 6 D 04:17:0.00 TODO: * Catch garbled input strings that might confuse the parser. * Create an iterable class to handle slices, min, max, sums, average, mean and stddev * More testing Homepage: http://statz.com/libs-TimeDuration/ Author : Andrew Lee (fiacre.patrick - at - gmail.com) -- http://mail.python.org/mailman/listinfo/python-announce-list Support the Python Software Foundation: http://www.python.org/psf/donations.html
Re: Can't do a multiline assignment!
[EMAIL PROTECTED] wrote: Yuck! No way!! If you *want* to make your code that hard to read, I'm sure you can find lots of ways to do so, even in Python, but don't expect Python to change to help you toward such a dubious goal. Well, my actual code doesn't look like that. Trust me, I like clean code. Seriously, examine your motivations for wanting such a syntax. Does it make the code more readable? (Absolutely not.) Does it make it more maintainable. (Certainly not -- consider it you needed to change CONSTANT2 to a different value some time in the future.) Use a dictionary? Yes, it makes it more readable. And yes, it does make it (a lot) more maintainable. Mainly because I don't have those four variables, I have about thirty. And I think I won't need to one or two of them, but maybe all of them at once. -- http://mail.python.org/mailman/listinfo/python-list
