升級到OSX 10.8 (Mountain Lion)後，pip使用遇到問題

升級之後，使用pip安裝套件，卻出現下面這種狀況。

Traceback (most recent call last):
  File "/usr/local/bin/pip", line 5, in 
    from pkg_resources import load_entry_point
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources.py", line 2603, in 
    working_set.require(__requires__)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources.py", line 666, in require
    needed = self.resolve(parse_requirements(requirements))
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources.py", line 565, in resolve
    raise DistributionNotFound(req)  # XXX put more info here
pkg_resources.DistributionNotFound: pip==1.1

這時候要做的事情很容易，只需要把pip做升級，就可以解決這個問題。

sudo easy_install -U pip

Reference: stackoverflow