Using python on OS X Lion

[Ned Deily]

In article 
<CAGZ55DT6XqbrDt-vwgcZsySTyZ=_QxHzPc8f=X0NMRs=fCtT=w at mail.gmail.com>,
 Johann Spies <johann.spies at gmail.com> wrote:
> I have recently upgraded my Snow Leopard to Lion and now I am having all
> problems with python on my system e.g.:
> 
> I have install PIL with easy_install but when I do
> 
> import PIL
> 
> Python cannot find the pil library. Installing psycopg2 in the same way was
> successful and I can use psycopg2 without a problem.
> 
> Further, the new version of Python is 2.7.1 in Lion.  But when I  just run
> 'python'  it calls up 2.6.5 - even after I have moved the application
> python2.6 to Trash.
> 
> I see several guidelines for using python on OS X: some using macports,
> others homebrew and others 'pip'  and 'virtualenv' .  I come from a Linux
> background where a proper packaging system like apt (on Debian) prevent
> these types of problems.
> 
> So my question:  What is the recommended way of setting up a python
> environment in OS X?
> 
> And how do I get rid of legacy python libraries on my system?

First, determine which python is being loaded.  In OS X 10.7 (Lion), 
Apple ships 2.7.1, 2.6.7, and 2.5.6 version of Python (all in /usr/bin) 
so the 2.6.5 is coming from elsewhere.  If you previously installed a 
Python from a python.org installer, the framework will be in 
/Library/Frameworks/Python.framework (and *not* 
/System/Library/Frameworks, which is where Apple's Pythons are and 
should not be modified).  The python.org installers, by default, may 
modify your shell profiles (i.e. .bash_profile, .profile, et al) to 
prepend its framework bin directory to your shell PATH.  Look for 
something like this:

# Setting PATH for MacPython 2.6
# The orginal version is saved in .profile.pysave
PATH="/Library/Frameworks/Python.framework/Versions/2.6/bin:${PATH}"
export PATH

There are more details here http://bugs.python.org/issue7107

Also understand that if you use easy_install or pip, each Python 
instance needs to have its own version of either one.  Apple supplies 
versions of easy_install in /usr/bin for its Pythons.  If you install 
another version of Python, you'll need to install another easy_install 
and pip for it as well.

-- 
 Ned Deily,
 nad at acm.org