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• How can I import the sqlite3 module into Python 2.4?

  - by Tony

  The sqlite3 module is included in Python version 2.5+. However, I am stuck with version 2.4. I uploaded the sqlite3 module files, added the directory to sys.path, but I get the following error when I try to import it: Traceback (most recent call last): File "<stdin>", line 1, in ? File "sqlite3/__init__.py", line 23, in ? from dbapi2 import * File "sqlite3/dbapi2.py", line 26, in ? from _sqlite3 import * ImportError: No module named _sqlite3 The file '_sqlite3' is in lib-dynload, but if I include this in the sqlite3 directory, I get additional errors. Any suggestions? I am working in a limited environment; I don't have access to GCC, among other things.

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• How to call a specific, unknown Python object attribute?

  - by Michael Morisy

  I'm working to create a simple Python script that will ultimately tell you how many blog entries were posted in a given month, and the pyblog app is proving very helpful. However, when I create the blog object, I don't know how to access it's various attributes. I can print them all out by printing one item from the dictionary, as shown (in excerpts) below: print blog.get_recent_posts(1) 'post_status': 'publish', 'date_created_gmt': <DateTime '20100601T19:27:17' at 2853300>, 'mt_excerpt': '', 'userid': '288', 'dateCreated': <DateTime '20100601T14:27:17' at 2853350>, 'custom_fields': [{'value': '', 'id': '1317', 'key': 'brightcove_code'}, {'value': 'http://bit.ly/d0Rywl', 'id': '1403', But how can I just get it to provide that DateTime information?

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• Java or Python distributed compute job (on a student budget)?

  - by midget_sadhu

  I have a large dataset (c. 40G) that I want to use for some NLP (largely embarrassingly parallel) over a couple of computers in the lab, to which i do not have root access, and only 1G of user space. I experimented with hadoop, but of course this was dead in the water-- the data is stored on an external usb hard drive, and i cant load it on to the dfs because of the 1G user space cap. I have been looking into a couple of python based options (as I'd rather use NLTK instead of Java's lingpipe if I can help it), and it seems distributed compute options look like: Ipython DISCO After my hadoop experience, i am trying to make sure i try and make an informed choice -- any help on what might be more appropriate would be greatly appreciated. Amazon's EC2 etc not really an option, as i have next to no budget.

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• Anyone Know a Great Sparse One Dimensional Array Library in Python?

  - by TheJacobTaylor

  I am working on an algorithm in Python that uses arrays heavily. The arrays are typically sparse and are read from and written to constantly. I am currently using relatively large native arrays and the performance is good but the memory usage is high (as expected). I would like to be able to have the array implementation not waste space for values that are not used and allow an index offset other than zero. As an example, if my numbers start at 1,000,000 I would like to be able to index my array starting at 1,000,000 and not be required to waste memory with a million unused values. Array reads and writes needs to be fast. Expanding into new territory can be a small delay but reads and writes should be O(1) if possible. Does anybody know of a library that can do it? Thanks!

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• Asking for input without stopping the script in python.

  - by ImTooStupidForThis

  I am (trying) to make a simple IRC client in python (as kind of a project while I learn the language). I have a loop that I use to receive and parse what the IRC server sends me, but if I use raw_input to input stuff, it stops the loop dead in its tracks until I input something (obviously). How can I input something without the loop stopping? Thanks in advance. (I don´t think I need to post the code, I just want to input something without the while 1 loop stopping.)

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• idiomatic way to take groups of n items from a list in Python?

  - by Wang

  Given a list A = [1 2 3 4 5 6] Is there any idiomatic (Pythonic) way to iterate over it as though it were B = [(1, 2) (3, 4) (5, 6)] other than indexing? That feels like a holdover from C: for a1,a2 in [ (A[i], A[i+1]) for i in range(0, len(A), 2) ]: I can't help but feel there should be some clever hack using itertools or slicing or something. (Of course, two at a time is just an example; I'd like a solution that works for any n.) Edit: related http://stackoverflow.com/questions/1162592/iterate-over-a-string-2-or-n-characters-at-a-time-in-python but even the cleanest solution (accepted, using zip) doesn't generalize well to higher n without a list comprehension and *-notation.

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• What's the most scalable way to handle somewhat large file uploads in a Python webapp?

  - by Jason Baker

  We have a web application that takes file uploads for some parts. The file uploads aren't terribly big (mostly word documents and such), but they're much larger than your typical web request and they tend to tie up our threaded servers (zope 2 servers running behind an Apache proxy). I'm mostly in the brainstorming phase right now and trying to figure out a general technique to use. Some ideas I have are: Using a python asynchronous server like tornado or diesel or gunicorn. Writing something in twisted to handle it. Just using nginx to handle the actual file uploads. It's surprisingly difficult to find information on which approach I should be taking. I'm sure there are plenty of details that would be needed to make an actual decision, but I'm more worried about figuring out how to make this decision than anything else. Can anyone give me some advice about how to proceed with this?

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• How do I change my current directory from a python script?

  - by misterloogs

  I'm trying to implement my own version of the 'cd' command that presents the user with a list of hard-coded directories to choose from, and the user has to enter a number corresponding to an entry in the list. The program, named my_cd.py for now, should then effectively 'cd' the user to the chosen directory. Example of how this should work: /some/directory $ my_cd.py 1) ~ 2) /bin/ 3) /usr Enter menu selection, or q to quit: 2 /bin $ Currently, I'm trying to 'cd' using os.chdir('dir'). However, this doesn't work, probably because my_cd.py is kicked off in its own child process. I tried wrapping the call to my_cd.py in a sourced bash script named my_cd.sh: #! /bin/bash function my_cd() { /path/to/my_cd.py } /some/directory $ . my_cd.sh $ my_cd ... shows list of dirs, but doesn't 'cd' in the interactive shell Any ideas on how I can get this to work? Is it possible to change my interactive shell's current directory from a python script?

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• Python - what's your conventions to declare your attributes in a class ?

  - by SeyZ

  Hello, In Python, I can declare attributes all over the class. For example : class Foo: def __init__(self): self.a = 0 def foo(self): self.b = 0 It's difficult to retrieve all attributes in my class when I have a big class with a lot of attributes. Is it better to have the following code (a) or the next following code (b) : a) Here, it's difficult to locate all attributes : class Foo: def __init__(self): foo_1() foo_2() def foo_1(self): self.a = 0 self.b = 0 def foo_2(self): self.c = 0 b) Here, it's easy to locate all attributes but is it beautiful ? class Foo: def __init__(self): (self.a, self.b) = foo_1() self.c = foo_2() def foo_1(self): a = 0 b = 0 return (a, b) def foo_2(self): c = 0 return c In a nutshell, what is your conventions to declare your attributes in a class ?

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• Python - Flatten a dict of lists into unique values?

  - by Jonathan Vanasco

  I have a dict of lists in python: content = {88962: [80, 130], 87484: [64], 53662: [58,80]} I want to turn it into a list of the unique values [58,64,80,130] I wrote a manual solution, but it's a manual solution. I know there are more concise and more elegant way to do this with list comprehensions, map/reduce , itertools , etc. anyone have a clue ? content = {88962: [80, 130], 87484: [64], 53662: [58,80]} result = set({}) for k in content.keys() : for i in content[k]: result.add(i) # and list/sort/print just to compare the output r2 = list( result ) r2.sort() print r2

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• Why doesn't Python's `re.split()` split on zero-length matches?

  - by Tim Pietzcker

  One particular quirk of the (otherwise quite powerful) re module in Python is that re.split() will never split a string on a zero-length match, for example if I want to split a string along word boundaries: >>> re.split(r"\s+|\b", "Split along words, preserve punctuation!") ['Split', 'along', 'words,', 'preserve', 'punctuation!'] instead of ['', 'Split', 'along', 'words', ',', 'preserve', 'punctuation', '!'] Why does it have this limitation? Is it by design? Do other regex flavors behave like this?

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• Python: How To copy function parameters into object's fields effortlessly ?

  - by bandana

  Many times I have member functions that copy parameters into object's fields. For Example: class NouveauRiches(object): def __init__(self, car, mansion, jet, bling): self.car = car self.mansion = mansion self.jet = jet self.bling = bling Is there a python language construct that would make the above code less tedious? One could use *args: def __init__(self, *args): self.car, self.mansion, self.jet, self.bling = args +: less tedious -: function signature not revealing enough. need to dive into function code to know how to use function -: does not raise a TypeError on call with wrong # of parameters (but does raise a ValueError) Any other ideas? (Whatever your suggestion, make sure the code calling the function does stays simple)

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• Whats the python way for recursively setting file permissions?

  - by Geoff

  What's the "python way" to recursively set the owner and group to files in a directory? I could just pass a 'chown -R' command to shell, but I feel like I'm missing something obvious. I'm mucking about with this: import os path = "/tmp/foo" for root, dirs, files in os.walk(path): for momo in dirs: os.chown(momo, 502, 20) This seems to work for setting the directory, but fails when applied to files. I suspect the files are not getting the whole path, so chown fails since it can't find the files. The error is: 'OSError: [Errno 2] No such file or directory: 'foo.html' What am I overlooking here?

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• Is it inefficient to access a python class member container in a loop statement?

  - by Dave

  Hi there. I'm trying to adopt some best practices to keep my python code efficient. I've heard that accessing a member variable inside of a loop can incur a dictionary lookup for every iteration of the loop, so I cache these in local variables to use inside the loop. My question is about the loop statement itself... if I have the following class: class A(object): def init(self) self.myList = [ 'a','b','c', 'd', 'e' ] Does the following code in a member function incur one, or one-per-loop-iteration (5) dictionary lookups? for letter in self.myList: print letter IE, should I adopt the following pattern, if I am concerned about efficiency... localList = self.myList for letter in localList: print letter or is that actually LESS efficient due to the local variable assign? Note, I am aware that early optimization is a dangerous pitfall if I'm concerned about the overall efficiency of code development. Here I am specifically asking about the efficiency of the code, not the coding. Thanks in advance! D

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• Do Managers in Python Multiprocessing module lock the shared data?

  - by AnonProcess

  This Question has been asked before: http://stackoverflow.com/questions/2936626/how-to-share-a-dictionary-between-multiple-processes-in-python-without-locking However I have several doubts regarding the program given in the answer: The issue is that the following step isn't atomic d['blah'] += 1 Even with locking the answer provided in that question would lead to random results. Since Process 1 read value of d['blah'] saves it on the stack increments it and again writes it. In Between a Process 2 can read the d['blah'] as well. Locking means that while d['blah'] is being written or read no other process can access it. Can someone clarify my doubts?

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• Python subprocess.Popen hangs in 'for l in p.stdout' until p terminates, why?

  - by Albert

  I have that code: #!/usr/bin/python -u localport = 9876 import sys, re, os from subprocess import * tun = Popen(["./newtunnel", "22", str(localport)], stdout=PIPE, stderr=STDOUT) print "** Started tunnel, waiting to be ready ..." for l in tun.stdout: sys.stdout.write(l) if re.search("Waiting for connection", l): print "** Ready for SSH !" break The "./newtunnel" will not exit, it will constantly output more and more data to stdout. However, that code will not give any output and just keeps waiting in the tun.stdout. When I kill the newtunnel process externally, it flushes all the data to tun.stdout. So it seems that I can't get any data from the tun.stdout while it is still running. Why is that? How can I get the information? Note that the default bufsize for Popen is 0 (unbuffered). I can also specify bufsize=0 but that doesn't change anything.

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• Python: How can I override one module in a package with a modified version that lives outside the pa

  - by zlovelady

  I would like to update one module in a python package with my own version of the module, with the following conditions: I want my updated module to live outside of the original package (either because I don't have access to the package source, or because I want to keep my local modifications in a separate repo, etc). I want import statements that refer to original package/module to resolve to my local module Here's an example of what I'd like to do using specifics from django, because that's where this problem has arisen for me: Say this is my project structure django/ ... the original, unadulterated django package ... local_django/ conf/ settings.py myproject/ __init__.py myapp/ myfile.py And then in myfile.py # These imports should fetch modules from the original django package from django import models from django.core.urlresolvers import reverse # I would like this following import statement to grab a custom version of settings # that I define in local_django/conf/settings.py from django.conf import settings def foo(): return settings.some_setting Can I do some magic with the __import__ statement in myproject/__init__.py to accomplish this? Is there a more "pythonic" way to achieve this?

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• How do I delete a curse window in python and restore background window?

  - by Zloy Smiertniy

  Hell-o guys, I'm working on python curses and I have my initial window with initscr() and I create several new windows to overlap it, I want to know if I can delete these windows and restore the standard screen without having to refill it. Is there a way? I can also ask if someone can tell me the difference between a window, subwindow, pad and sub pad. I have this code: stdscr = curses.initscr() Then I fill it with random letters stdscr.refresh() newwin=curses.newwin(10,20,5,5) newwin.touchwin() newwin.refresh() I want to delete newwin here so that if I write stdscr.refresh() newwin won't appear stdscr.touchwin() stdscr.refresh() And here it should appear as if no window was created.

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• Rounding issue when adding floats in python, is this normal?

  - by thepearson

  I just wanted to know if this behavior is expected. If so, can someone explain to me why. This has probably been answered elsewhere I can't seem to find it using Google. Probably not searching with the right terms. I am running Ubuntu 10.04. Python 2.6.5 (r265:79063, Apr 16 2010, 13:09:56) [GCC 4.4.3] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> var = 10.0 >>> var 10.0 >>> var + 5 15.0 >>> var + 5.1 15.1 >>> var + 5.2 15.199999999999999 >>>

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• Is there a difference between `==` and `is` in python?

  - by Bernard

  My Google-fu has failed me. In Python, are these: n = 5 # Test one. if n == 5: print 'Yay!' # Test two. if n is 5: print 'Yay!' two tests for equality equivalent (ha!)? Does this hold true for objects where you would be comparing instances (a list say)? Okay, so this kind of answers my question: l = list() l.append(1) if l == [1]: print 'Yay!' # Holds true, but... if l is [1]: print 'Yay!' # Doesn't. So == tests value where is tests to see if they are the same object?

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• How should I build a simple database package for my python application?

  - by Carson Myers

  I'm building a database library for my application using sqlite3 as the base. I want to structure it like so: db/ __init__.py users.py blah.py etc.py So I would do this in Python: import db db.users.create('username', 'password') I'm suffering analysis paralysis (oh no!) about how to handle the database connection. I don't really want to use classes in these modules, it doesn't really seem appropriate to be able to create a bunch of "users" objects that can all manipulate the same database in the same ways -- so inheriting a connection is a no-go. Should I have one global connection to the database that all the modules use, and then put this in each module: #users.py from db_stuff import connection Or should I create a new connection for each module and keep that alive? Or should I create a new connection for every transaction? How are these database connections supposed to be used? The same goes for cursor objects: Do I create a new cursor for each transaction? Create just one for each database connection?

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• How do I build a python string from a raw (binary) ctype buffer?

  - by fcrazy

  I'm playing with Python and ctypes and I can't figure out how to resolve this problem. I call to a C function which fills a raw binary data. My code looks like this: class Client(): def __init__(self): self.__BUFSIZE = 1024*1024 self.__buf = ctypes.create_string_buffer(self.__BUFSIZE) self.client = ctypes.cdll.LoadLibrary(r"I:\bin\client.dll") def do_something(self): len_written = self.client.fill_raw_buffer(self.__buf, self.__BUFSIZE) my_string = repr(self.__buf.value) print my_string The problem is that I'm receiving binary data (with 0x00) and it's truncated when I tried to build my_string. How can I build my_string if self._buf contains null bytes 0x00? Any idea is welcome. Thanks

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• How to input test data using the DecisionTree module in python?

  - by lifera1n

  On the Python DescisionTree module homepage (DecisionTree-1.6.1), they give a piece of example code. Here it is: dt = DecisionTree( training_datafile = "training.dat", debug1 = 1 ) dt.get_training_data() dt.show_training_data() root_node = dt.construct_decision_tree_classifier() root_node.display_decision_tree(" ") test_sample = ['exercising=>never', 'smoking=>heavy', 'fatIntake=>heavy', 'videoAddiction=>heavy'] classification = dt.classify(root_node, test_sample) print "Classification: ", classification My question is: How can I specify sample data (test_sample here) from variables? On the project homepage, it says: "You classify new data by first constructing a new data vector:" I have searched around but have been unable to find out what a data vector is or the answer to my question. Any help would be appreciated!

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• how could it works if function is called before it is defined in python?

  - by user2131316

  I was wondering what does if __name__ == "__main__": really do in python, I have the following code in python3: def main(): test(); def test(): print("hello world " + __name__); if __name__ == "__main__": main(); we know that we have to declare a function before we use it, so function call inside of if part works fine, the main() is defined before it is called inside of if statement, but what about the test() function, it is defined after it is called and there is no errors: def main(): test(); def test(): print("hello world " + __name__); so how could it works if the test() function is defined after it is called?

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• How to enter decimal/binary numbers when creating byte objects in python?

  - by Eric

  I'm using python 3.1.1. I know that I can create byte objects using the byte literal in the form of b'...'. In these byte objects, each byte can be represented as a character(in ascii code if I'm not wrong) or as a hexadecimal/octal number. Hexadecimal and octal numbers can be entered using an escape of \x for hexadecimal numbers and just a \ for octal numbers. However, there's no escape sequences for decimal or binary numbers. Is there any way to enter them into byte objects?

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