Is the order reported by 'sys.path' the order in which packages are searched?

问题

Does the order in which entries occur in the Python sys.path correspond to the order in which packages are found? For example I have

>>> from pprint import pprint     
>>> pprint(sys.path)
['',
 '/Library/Python/2.7/site-packages/ipython-0.14.dev-py2.7.egg',
 '/Library/Python/2.7/site-packages/matplotlib-1.3.x-py2.7-macosx-10.8-intel.egg',
 '/Library/Python/2.7/site-packages/numpy-1.8.0.dev_3abd869_20121222-py2.7-macosx-10.8-intel.egg',
 '/Library/Python/2.7/site-packages/pymc-2.2-py2.7-macosx-10.8-intel.egg',
 '/Library/Python/2.7/site-packages/scikit_learn-0.13_git-py2.7-macosx-10.8-intel.egg',
 '/Library/Python/2.7/site-packages/scipy-0.12.0.dev_d631749_20121222-py2.7-macosx-10.8-intel.egg',
 '/Library/Python/2.7/site-packages/statsmodels-0.5.0-py2.7-macosx-10.8-intel.egg',
 '/Library/Python/2.7/site-packages/readline-6.2.4.1-py2.7-macosx-10.7-intel.egg',
 '/Library/Python/2.7/site-packages/nose-1.2.1-py2.7.egg',
 '/Library/Python/2.7/site-packages/six-1.2.0-py2.7.egg',
 '/Library/Python/2.7/site-packages/tornado-2.4.1-py2.7.egg',
 '/Library/Python/2.7/site-packages/pyzmq-2.2.0.1-py2.7-macosx-10.8-intel.egg',
 '/Library/Python/2.7/site-packages/patsy-0.1.0-py2.7.egg',
 '/Library/Python/2.7/site-packages/pip-1.2.1-py2.7.egg',
 '/Library/Python/2.7/site-packages/xattr-0.6.4-py2.7-macosx-10.8-intel.egg',
 '/Library/Python/2.7/site-packages/distribute-0.6.28-py2.7.egg',
 '/Library/Python/2.7/site-packages/astropy-0.3.dev2837-py2.7-macosx-10.8-intel.egg',
 '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python27.zip',
 '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7',
 '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/plat-darwin',
 '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/plat-mac',
 '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/plat-mac/lib-scriptpackages',
 '/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python',
 '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-tk',
 '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-old',
 '/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-dynload',
 '/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/PyObjC',
 '/Library/Python/2.7/site-packages']

so that, in general, I've got

['',
 '/Library/Python/2.7/site-packages/PKG_WITH_EGG.egg',
 ...
 '/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python',
 ...
 '/Library/Python/2.7/site-packages']

Does that mean that if a package I install (in 'site-packages') happens to have a .egg, it will supersede a version of the same package that might be in 'Extras' but that those (in 'site-packages') that do not have an .egg will be superseded by any version in 'Extras'?

来源：https://stackoverflow.com/questions/14882377/is-the-order-reported-by-sys-path-the-order-in-which-packages-are-searched

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