Python
Contents
Intro
This cheat sheet helps troubleshoot common problems...
Some good documentation source:
- http://www.python.org/doc/2.5.4/download/
- apprendre a programmer avec python by gerard swinnen (french, free PDF on the net)
Tricks
Importing
X = __import__(‘X’)
works like
import X
with the difference that you 1) pass the module name as a string, and 2) explicitly assign it to a variable in your current namespace.
Content of objects
Finding what's in an object
>>> dir(obj)
Copying objects
Regular:
obj2 = obj1
Complete:
obj2 = copy.deepcopy(obj1)
Key, Values of dicts
ah iteritems() ...
>>> knights = {'gallahad': 'the pure', 'robin': 'the brave'}
>>> for k, v in knights.iteritems():
... print k, v
Any kind of garbage
.strip(string.whitespace + string.punctuation)
Glob me baby! File completion in a snap
self.list = glob.glob("*.db")
Getting content AND index from lists
for index,line in enumerate(content):
...
Debugging
See http://pythonconquerstheuniverse.wordpress.com/category/the-python-debugger/
import pdb pdb.set_trace()
Editor tricks
Emacs
See http://python.about.com/b/2007/09/24/emacs-tips-for-python-programmers.htm
- C-c <: Shift the region to the left
- C-c >: Shift the region to the right
HOW TO
Modules & Extensions: distutils
One mention, sometime you get this error message when building your extension under Mac OS X:
/usr/bin/ld: can't locate file for: -lnameofmylib
This seems to be a weird problem with Mac OS X where even if the library (here a dynamic library ending with .dylib) is in /usr/lib, it won't be "seen" by the ld linker. To mitigate this problem, create a link in /usr/local/lib/ to the /usr/lib/XXXX.dylib library and add the path in the setup.py file.
Here is a sample setup.py that fixes that:
"""
setup.py
Created by Philippe Langlois on 2009-11-02.
Copyright (c) 2009 Philippe Langlois. All rights reserved.
"""
from distutils.core import setup, Extension
setup(name='pysctp',
version='0.5',
py_modules=['sctp'],
ext_modules=[Extension('pysctp', sources=['_sctp.c'],
include_dirs=['.', '/usr/include'],
libraries=['sctp'],
library_dirs=['/usr/lib/', '/usr/local/lib/'],
)
],
data_files=['_sctp.h'],
author='Elvis Pfutzenreuter',
author_email='epx __AAAAATTTT_____ epx.com.br',
maintainer='Philippe Langlois',
maintainer_email='Philippe.Langlois __AAAAATTT____ gmail.com',
)
Problems
I installed some modules / packages and can't load them
echo $PYTHONPATH
$ python
Python 2.5.2 (r252:60911, Feb 22 2008, 07:57:53)
[GCC 4.0.1 (Apple Computer, Inc. build 5363)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
for i in sys.path:
print i
You can add a .pth file in one of the already loaded dir: see http://djangotricks.blogspot.com/2008/09/note-on-python-paths.html
like:
# cat > /Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5/site-packages/others.pth /Library/Python/2.5/site-packages/ ^D
Good packages / extensions
dpkt
For bit-manipulation in python
