[Distutils] A quick question on pkg_resources.find_distributions

[Phillip J. Eby]

At 01:07 PM 7/13/2005 +0100, Paul Moore wrote:
>I have only one egg installed in my site-packages, namely setuptools.
>However, with the following script:
>
>import sys
>import pkg_resources
>
>def list_packages():
>     dists = []
>     for p in sys.path:
>         for dist in pkg_resources.find_distributions(p):
>             dists.append((p, dist))
>
>     for p, dist in dists:
>         print p, dist.name, dist.version
>
>if __name__ == '__main__':
>     list_packages()
>
>I get the output:
>
>C:\Apps\Python24\lib\site-packages setuptools 0.5a12
>C:\Apps\Python24\Lib\site-packages\setuptools-0.5a12-py2.4.egg setuptools 
>0.5a12
>
>How come I see setuptools twice?

You need to look at the .path attributes.  What's happening is that 
setuptools is on sys.path directly, but it's also in a *directory* on 
sys.path.  So, you're calling find_distributions() on site-packages, but 
you're also calling it directly on the egg, so you get it twice.

In the future, I may separate these kinds of returns, such that there's a 
way to ask find_distributions() to give you only exact matches, because 
this will be needed for implementing the WorkingSet concept in the 
pkg_resources refactoring.


>A complementary question - how can I detect when two Distribution
>instances refer to the "same" egg. Is comparing the path attribute
>sufficient?

You need os.path.normcase on Windows, and 
os.path.normpath/os.path.realpath/etc. to be really sure.  Sane path 
comparison is unfortunately somewhat of a black art in Python.