Here's a simple bash oneliner to determine the installation prefix (and more) of a python interpreter:

python -c 'import sys;print("\n".join("{0:16s}: {1!r}".format(x, getattr(sys, x)) for x in ["executable", "version", "prefix", "exec_prefix"]))'

(Replace "python" with the actual python executable you want to investigate of course)

Example result:

executable      : '/Library/Frameworks/Python.framework/Versions/2.7/Resources/'
version         : '2.7 (r27:82508, Jul  3 2010, 21:12:11) \n[GCC 4.0.1 (Apple Inc. build 5493)]'
prefix          : '/Library/Frameworks/Python.framework/Versions/2.7'
exec_prefix     : '/Library/Frameworks/Python.framework/Versions/2.7'

I have multiple (too much actually) python interpreters on my mac, and this oneliner helps to keep a bit of overview.