Как узнать из какого каталога Python использует библиотеку? (import xxx)

$ python

Python 2.6.7 (r267:88850, Oct  8 2011, 08:42:47)
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.

>>> import PyQt4
>>> PyQt4

<module 'PyQt4' from '/Users/michael_xiii/Envs/py26/lib/python2.6/site-packages/PyQt4/__init__.py'>