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• Perl for a Python programmer

  - by fortran

  I know Python (and a bunch of other languages) and I think it might be nice to learn Perl, even if it seems that most of the people is doing it the other way around... My main concern is not about the language itself (I think that part is always easy), but about learning the Perlish (as contrasted with Pythonic) way of doing things; because I don't think it'll be worth the effort if I end up programming Python in Perl. So my questions are basically two: Are there many problems/application areas where it's actually more convenient to solve them in Perl rather than in Python? If the first question is positive, where can I found a good place to get started and learn best practices that is not oriented to beginners?

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• Python 'datetime.datetime' object is unsubscriptable

  - by Robert

  First, I am NOT a python developer. I am trying to fix an issue within a python script that is being executed from the command line. This script was written by someone who is no longer around, and no longer willing to help with issues. This is python 2.5, and for the moment it cannot be upgraded. Here are the lines of code in question: start_time = datetime.strptime(str(paf.Start),"%Y-%m-%d %H:%M:%S") dict_start = datetime(*start_time[:6]) end_time = datetime.strptime(str(paf.End),"%Y-%m-%d %H:%M:%S") dict_end = datetime(*end_time[:6]) When this code is ran, it generates an error with the description: 'datetime.datetime' object is unsubscriptable. This is the import statement: from datetime import datetime I have a feeling that this is something simple, but not being my native language and Google not yielding any valuable results, I am stuck. I have tried a couple of different import methods, yielding different errors, but all with these statements. Any help on this would be greatly appreciated.

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• php vs python. scalability

  - by Quamis

  Why is PHP considered more scalable than python? I've heard may times that one of the reasons PHP is "better" than python is that PHP is more easily scalable, and that Yahoo proves that(assumig Yahoo still uses PHP). Whats the difference between PHP and Python when it comes to scalability? -- edit -- well, i have no evidence, the question arose after a discussion with a friend. -- edit2 -- here: http://www.oreillynet.com/ruby/blog/2007/09/7%5Freasons%5Fi%5Fswitched%5Fback%5Fto%5Fp%5F1.html , even if this dosent say anything about scaling..

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• Webdriver python bindings

  - by Ockonal

  Hello, I can't make python bindings for webdriver workable. Here is tutorial for installing. easy_install webdriver Won't find webdriver package so I have to install it manually from sources. I've downloaded source from trunk, set WEBDRIVER and PYTHONPATH variables and installed webdriver: ~$ cd ~ ~$ svn checkout http://selenium.googlecode.com/svn/trunk/ selenium-read-only ~$ cd selenium-read-only ~# python setup.py install ~$ env |grep PYT ~$> PYTHONPATH=:/home/ockonal/selenium-read-only/../../../firefox/lib-src:/home/ockonal/selenium-read-only/.. ~$ env |grep WEB ~$> WEBDRIVER=/home/ockonal/selenium-read-only Then I downloaded RemoteDriverServer.jar and ran it: java -jar RemoteDriverServer.jar 8888 Now I want to include webdriver module in python script: from selenium.firefox.webdriver import WebDriver ImportError: No module named firefox.webdriver

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• Python serialize lexical closures?

  - by dsimcha

  Is there a way to serialize a lexical closure in Python using the standard library? pickle and marshal appear not to work with lexical closures. I don't really care about the details of binary vs. string serialization, etc., it just has to work. For example: def foo(bar, baz) : def closure(waldo) : return baz * waldo return closure I'd like to just be able to dump instances of closure to a file and read them back. Edit: One relatively obvious way that this could be solved is with some reflection hacks to convert lexical closures into class objects and vice-versa. One could then convert to classes, serialize, unserialize, convert back to closures. Heck, given that Python is duck typed, if you overloaded the function call operator of the class to make it look like a function, you wouldn't even really need to convert it back to a closure and the code using it wouldn't know the difference. If any Python reflection API gurus are out there, please speak up.

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• Python urllib.urlopen IOError

  - by Michael

  So I have the following lines of code in a function sock = urllib.urlopen(url) html = sock.read() sock.close() and they work fine when I call the function by hand. However, when I call the function in a loop (using the same urls as earlier) I get the following error: > Traceback (most recent call last): File "./headlines.py", line 256, in <module> main(argv[1:]) File "./headlines.py", line 37, in main write_articles(headline, output_folder + "articles_" + term +"/") File "./headlines.py", line 232, in write_articles print get_blogs(headline, 5) File "/Users/michaelnussbaum08/Documents/College/Sophmore_Year/Quarter_2/Innovation/Headlines/_code/get_content.py", line 41, in get_blogs sock = urllib.urlopen(url) File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/urllib.py", line 87, in urlopen return opener.open(url) File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/urllib.py", line 203, in open return getattr(self, name)(url) File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/urllib.py", line 314, in open_http if not host: raise IOError, ('http error', 'no host given') IOError: [Errno http error] no host given Any ideas?

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• Using Python to call Mencoder with some arguments

  - by Manu

  Hello, I'll start by saying that I am very, very new to Python. I used to have a Windows/Dos batch file in order to launch Mencoder with the right set of parameters, without having to type them each time. Things got messy when I tried to improve my script, and I decided that it would be a good opportunity to try coding something in python. I've come up with that : #!/usr/bin/python import sys, os #Path to mencoder mencoder = "C:\Program Files\MPlayer-1.0rc2\mencoder.exe" infile = "holidays.avi" outfile = "holidays (part1).avi" startTime = "00:48:00" length = "00:00:15" commande = "%s %s -ovc copy -oac copy -ss %s -endpos %s -o %s" os.system(commande % (mencoder, infile, startTime, length, outfile)) #Pause raw_input() But that doesn't work, windows complains that "C:\Program" is not recognized command. I've trying putting some "\"" here and there, but that didn't help.

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• OpenCV 2.0 and Python

  - by Jive Dadson

  I cannot get the example Python programs to run. When executing the Python command "from opencv import cv" I get the message "ImportError: No module named _cv". There is a stale _cv.pyd in the site-packages directory, but no _cv.py anywhere. See step 5 below. MS Windows XP, VC++ 2008, Python 2.6, OpenCV 2.0 Here's what I have done. Downloaded and ran the MS Windows installer for OpenCV2.0. Downloaded and installed CMake Downloaded and installed SWIG Ran CMake. After unchecking "ENABLE_OPENMP" in the CMake GUI, I was able to build OpenCV using INSTALL.vcproj and BUILD_ALL.vcproj. I do not know what the difference is, so I built everything under both of those project files. The C example programs run fine. Copied contents of OpenCV2.0/Python2.6/lib/site-packages to my installed Python2.6/lib/site-packages directory. I notice that it contains an old _cv.pyd and an old libcv.dll.a.

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• Pointer argument to boost python

  - by piotr

  What's the best way to make a function that has pointer as argument work with boost python? I see there are many possibilities for return values in the docs, but I don't know how to do it with arguments. void Tesuto::testp(std::string* s) { if (!s) cout << " NULL s" << endl; else cout << s << endl; } >>> t.testp(None) NULL s >>> >>> s='test' >>> t.testp(s) Traceback (most recent call last): File "<stdin>", line 1, in <module> Boost.Python.ArgumentError: Python argument types in Tesuto.testp(Tesuto, str) did not match C++ signature: testp(Tesuto {lvalue}, std::string*) >>>

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• functional-style datatypes in Python

  - by Danny Roberts

  For anyone who's spent some time with sml, ocaml, haskell, etc. when you go back to using C, Python, Java, etc. you start to notice things you never knew were missing. I'm doing some stuff in Python and I realized what I really want is a functional-style datatype like (for example) datatype phoneme = Vowel of string | Consonant of voice * place * manner datatype voice = Voiced | Voiceless datatype place = Labial | Dental | Retroflex | Palatal | Velar | Glottal datatype manner = Stop | Affricate | Fricative | Nasal | Lateral type syllable = phoneme list Does anyone have a particular way that they like to simulate this in Python?

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• Python regular expression implementation details

  - by Tom

  A question that I answered got me wondering: How are regular expressions implemented in Python? What sort of efficiency guarantees are there? Is the implementation "standard", or is it subject to change? I thought that regular expressions would be implemented as DFAs, and therefore were very efficient (requiring at most one scan of the input string). Laurence Gonsalves raised an interesting point that not all Python regular expressions are regular. (His example is r"(a+)b\1", which matches some number of a's, a b, and then the same number of a's as before). This clearly cannot be implemented with a DFA. So, to reiterate: what are the implementation details and guarantees of Python regular expressions? It would also be nice if someone could give some sort of explanation (in light of the implementation) as to why the regular expressions "cat|catdog" and "catdog|cat" lead to different search results in the string "catdog", as mentioned in the question that I referenced before.

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• How to parse malformed HTML in python, using standard libraries

  - by bukzor

  There are so many html and xml libraries built into python, that it's hard to believe there's no support for real-world HTML parsing. I've found plenty of great third-party libraries for this task, but this question is about the python standard library. Requirements: Use only Python standard library components (I'm currently using v2.6) DOM support Handle HTML entities (&nbsp;) Handle partial documents (like: Hello, <iWorld</i!) Bonus points: XPATH support Handle unclosed/malformed tags. (<bigdoes anyone here know <html ???

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• Python and Postgresql

  - by Ian

  Hi all, if you wanted to manipulate the data in a table in a postgresql database using some python (maybe running a little analysis on the result set using scipy) and then wanted to export that data back into another table in the same database, how would you go about the implementation? Is the only/best way to do this to simply run the query, have python store it in an array, manipulate the array in python and then run another sql statement to output to the database? I'm really just asking, is there a more efficient way to deal with the data? Thanks, Ian

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• Newbie Python programmer tangling with Lists.

  - by Sergio Tapia

  Here's what I've got so far: # A. match_ends # Given a list of strings, return the count of the number of # strings where the string length is 2 or more and the first # and last chars of the string are the same. # Note: python does not have a ++ operator, but += works. def match_ends(words): counter = 0 for word in words: if len(word) >= 2 and word[0] == word[-1]: counter += counter return counter # +++your code here+++ return I'm following the Google Python Class, so this isn't homework, but me just learning and improving myself; so please no negative comments about 'not doing my homework'. :P What do you guys think I'm doing wrong here? Here's the result: match_ends X got: 0 expected: 3 X got: 0 expected: 2 X got: 0 expected: 1 I'm really loving Python, so I just know that I'll get better at it. :)

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• Python 3.1.1 Problem With Tuples

  - by Protean

  This piece of code is supposed to go through a list and preform some formatting to the items, such as removing quotations, and then saving it to another list. class process: def rchr(string_i, asciivalue): string_o = () for i in range(len(string_i)): if ord(string_i[i]) != asciivalue: string_o += string_i[i] return string_o def flist(self, list_i): cache = () cache_list = [] for line in list_i: cache = line.split('\t') cacbe[0] = process.rchr(str(cache[0]), 34) cache_list.append(cache[0]) cache_list[index] = cache index += 1 cache_list.sort() return cache_list p = process() list1a = ['cow', 'dog', '"sheep"'] list1 = p.flist(list1a) print (country_list) However; it chokes at 'string_o += string_i[i]' and gives the following error: Traceback (most recent call last): File "/Projects/Python/safafa.py", line 23, in <module> list1 = p.flist(list1a) File "/Projects/Python/safafa.py", line 14, in flist cacbe[0] = process.rchr(str(cache[0]), 34) File "/Projects/Python/safafa.py", line 7, in rchr string_o += string_i[i] TypeError: can only concatenate tuple (not "str") to tuple

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• Getting Started with Python: Attribute Error

  - by Nacari

  I am new to python and just downloaded it today. I am using it to work on a web spider, so to test it out and make sure everything was working, I downloaded a sample code. Unfortunately, it does not work and gives me the error: "AttributeError: 'MyShell' object has no attribute 'loaded' " I am not sure if the code its self has an error or I failed to do something correctly when installing python. Is there anything you have to do when installing python like adding environmental variables, etc.? And what does that error generally mean? Here is the sample code I used with imported spider class: import chilkat spider = chilkat.CkSpider() spider.Initialize("www.chilkatsoft.com") spider.AddUnspidered("http://www.chilkatsoft.com/") for i in range(0,10): success = spider.CrawlNext() if (success == True): print spider.lastUrl() else: if (spider.get_NumUnspidered() == 0): print "No more URLs to spider" else: print spider.lastErrorText() # Sleep 1 second before spidering the next URL. spider.SleepMs(1000)

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• ungetc in Python

  - by Dragos Toader

  Some file read (readlines()) functions in Python copy the file contents to memory (as a list) I need to process a file that's too large to be copied in memory and as such need to use a file pointer (to access the file one byte at a time) -- as in C getc(). The additional requirement I have is that I'd like to rewind the file pointer to previous bytes like in C ungetc(). Is there a way to do this in Python? Also, in Python, I can read one line at a time with readline() Is there a way to read the previous line going backward?

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• Reverse Engineer a .pyo python file

  - by Brian

  I have 2 .pyo python files that I can convert to .py source files, but they don't compile perfectly as hinted by decompyle's verify. Therefore looking at the source code, I can tell that config.pyo simply had variables in in an array: ADMIN_USERIDS = [116901, 141, 349244, 39, 1159488] I would like to take the original .pyo and disassembly or whatever I need to do inorder to change one of these IDs. Or.... in model.pyo the source indicates a if (productsDeveloperId != self.getUserId()): All I would want to do is hex edit the != to be a == .....Simple with a windows exe program but I can't find a good python disassembler anywhere. Any suggestions are welcomed...I am new to reading bytecode and new to python as well.

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• Stochastic calculus library in python

  - by LeMiz

  Hello, I am looking for a python library that would allow me to compute stochastic calculus stuff, like the (conditional) expectation of a random process I would define the diffusion. I had a look a at simpy (simpy.sourceforge.net), but it does not seem to cover my needs. This is for quick prototyping and experimentation. In java, I used with some success the (now inactive) http://martingale.berlios.de/Martingale.html library. The problem is not difficult in itself, but there is a lot non trivial, boilerplate things to do (efficient memory use, variable reduction techniques, and so on). Ideally, I would be able to write something like this (just illustrative): def my_diffusion(t, dt, past_values, world, **kwargs): W1, W2 = world.correlated_brownians_pair(correlation=kwargs['rho']) X = past_values[-1] sigma_1 = kwargs['sigma1'] sigma_2 = kwargs['sigma2'] dX = kwargs['mu'] * X * dt + sigma_1 * W1 * X * math.sqrt(dt) + sigma_2 * W2 * X * X * math.sqrt(dt) return X + dX X = RandomProcess(diffusion=my_diffusion, x0 = 1.0) print X.expectancy(T=252, dt = 1./252., N_simul= 50000, world=World(random_generator='sobol'), sigma1 = 0.3, sigma2 = 0.01, rho=-0.1) Does someone knows of something else than reimplementing it in numpy for example ?

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• Python: Why is IDLE so slow?

  - by Adam Matan

  Hi, IDLE is my favorite Python editor. It offers very nice and intuitive Python shell which is extremely useful for unit-testing and debugging, and a neat debugger. However, code executed under IDLE is insanely slow. By insanely I mean 3 orders of magnitude slow: bash time echo "for i in range(10000): print 'x'," | python Takes 0.052s, IDLE import datetime start=datetime.datetime.now() for i in range(10000): print 'x', end=datetime.datetime.now() print end-start Takes: >>> 0:01:44.853951 Which is roughly 2,000 times slower. Any thoughts, or ideas how to improve this? I guess it has something to do with the debugger in the background, but I'm not really sure. Adam

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• Python (windows) will open files from command line, but not from a script launched from eclipse

  - by Blake

  I'm pretty new to writing python for windows (linux is no problem), and am having problems getting python to recognize files when running scripts, though it behaves fine in the command line What am I doing wrong here? def verifyFile(x): # return os.path.isfile(x) This will return true (with a valid file, of course) when called from the python command line, but when I run the script from eclipse, or launch it from windows, it ALWAYS returns false. Any thoughts on why this is? I've tried passing pathnames like this: D:\Documents and Settings\BDE\Desktop\cdburn.jpg and like this: D:/Documents and Settings/BDE/Desktop/cdburn.jpg I've changed sys,argv[0] to '' I've tried this: def verifyFile(x): # try: f = open(x, 'r') f.close() return True except: return False and am getting no love! Any help would be appreciated. Thanks Blake

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• How do I use Python's itertools.groupby()?

  - by James Sulak

  I haven't been able to find an understandable explanation of how to actually use Python's itertools.groupby() function. What I'm trying to do is this: take a list - in this case, the children of an objectified lxml element - divide it into groups based on some criteria, and then later iterate over each of these groups separately. I've reviewed the documentation (http://docs.python.org/lib/itertools-functions.html), and the examples, (http://docs.python.org/lib/itertools-example.html), but I've had trouble trying to apply them beyond a simple list of numbers. So, how do I use of itertools.groupby()? Is there another technique I should be using? Pointers to good "prerequisite" reading would also be appreciated.

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• AES Encryption. From Python (pyCrypto) to .NET

  - by Why

  I am currently trying to port a legacy Python app over to .NET which contains AES encrpytion using from what I can tell pyCrpyto. I have very limited Python and Crypto experience. The code uses the snippet from the following page. http://www.djangosnippets.org/snippets/1095/ So far I believe I have managed to work out that it that it calls Crypto.Cipher with AES and the first 32 character of our secret key as the password, but no mode or IV. It also puts a prefix on the encrpyed text when it is added to database. What I can't work out is how I can decrypt the existing ecrypted database records in .NET. I have been looking at RijndaelManaged but it requires an IV and can't see any reference to one in python. Can anyone point me in the dirrection to what method could be used in .NET to get the desired result.

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• Tag Cloud library in Java

  - by Denzil

  I would like to know if there's an open source library (JAR) available to generate a tag-cloud in Java?

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• Pre-generating GUIDs for use in python?

  - by rjuiaa1

  I have a python program that needs to generate several guids and hand them back with some other data to a client over the network. It may be hit with a lot of requests in a short time period and I would like the latency to be as low as reasonably possible. Ideally, rather than generating new guids on the fly as the client waits for a response, I would rather be bulk-generating a list of guids in the background that is continually replenished so that I always have pre-generated ones ready to hand out. I am using the uuid module in python on linux. I understand that this is using the uuidd daemon to get uuids. Does uuidd already take care of pre-genreating uuids so that it always has some ready? From the documentation it appears that it does not. Is there some setting in python or with uuidd to get it to do this automatically? Is there a more elegant approach then manually creating a background thread in my program that maintains a list of uuids?

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