title: Problems with upgrading pip in Homebrew Python 2.7 installation
body: <p>I've got Python 2.7.9 installed using Homebrew on my Mac, and Homebrew also installs pip. There's also an older, unused version of Python that was installed by default on my Mac.</p>
  
  <p>The problem is that when I try to upgrade pip (using <code>pip install --upgrade pip</code>), pip seems to want to upgrade the version of pip that comes with the older, default version of Python. Here's what happens (after doing a fresh install of Python 2.7.9, i.e., <code>brew remove python</code> followed by <code>brew install python</code>):</p>
  
  <pre><code>$ pip -V
  pip 6.0.7 from /usr/local/Cellar/python/2.7.9/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/pip-6.0.7-py2.7.egg (python 2.7)
  </code></pre>
  
  <p>The above seems correct. However, the following happens:</p>
  
  <pre><code>$ pip install --upgrade pip
  You are using pip version 6.0.7, however version 6.0.8 is available.
  You should consider upgrading via the 'pip install --upgrade pip' command.
  Collecting pip from https://pypi.python.org/packages/py2.py3/p/pip/pip-6.0.8-py2.py3-none-any.whl#md5=41e73fae2c86ba2270ff51c1d86f7e09
    Using cached pip-6.0.8-py2.py3-none-any.whl
  Installing collected packages: pip
    Found existing installation: pip 6.0.7
      Uninstalling pip-6.0.7:
        Successfully uninstalled pip-6.0.7
  
  Successfully installed pip-1.4.1
  </code></pre>
  
  <p>Why was pip 1.4.1 installed? Now I get:</p>
  
  <pre><code>$ pip -V
  pip 1.4.1 from /Library/Python/2.7/site-packages/pip-1.4.1-py2.7.egg (python 2.7)
  </code></pre>
  
  <p>That seems to correspond to the older default version of Python. When I try to upgrade again, it fails:</p>
  
  <pre><code>$ pip install --upgrade pip
  Downloading/unpacking pip from https://pypi.python.org/packages/source/p/pip/pip-6.0.8.tar.gz#md5=2332e6f97e75ded3bddde0ced01dbda3
    Downloading pip-6.0.8.tar.gz (1.2MB): 1.2MB downloaded
    Running setup.py egg_info for package pip
  
      warning: no previously-included files found matching '.coveragerc'
      warning: no previously-included files found matching '.mailmap'
      warning: no previously-included files found matching '.travis.yml'
      warning: no previously-included files found matching 'pip/_vendor/Makefile'
      warning: no previously-included files found matching 'tox.ini'
      warning: no previously-included files found matching 'dev-requirements.txt'
      no previously-included directories found matching '.travis'
      no previously-included directories found matching 'docs/_build'
      no previously-included directories found matching 'contrib'
      no previously-included directories found matching 'tasks'
      no previously-included directories found matching 'tests'
  Installing collected packages: pip
    Found existing installation: pip 1.4.1
      Uninstalling pip:
  Cleaning up...
  Exception:
  Traceback (most recent call last):
    File "/Library/Python/2.7/site-packages/pip-1.4.1-py2.7.egg/pip/basecommand.py", line 134, in main
      status = self.run(options, args)
    File "/Library/Python/2.7/site-packages/pip-1.4.1-py2.7.egg/pip/commands/install.py", line 241, in run
      requirement_set.install(install_options, global_options, root=options.root_path)
    File "/Library/Python/2.7/site-packages/pip-1.4.1-py2.7.egg/pip/req.py", line 1294, in install
      requirement.uninstall(auto_confirm=True)
    File "/Library/Python/2.7/site-packages/pip-1.4.1-py2.7.egg/pip/req.py", line 525, in uninstall
      paths_to_remove.remove(auto_confirm)
    File "/Library/Python/2.7/site-packages/pip-1.4.1-py2.7.egg/pip/req.py", line 1639, in remove
      renames(path, new_path)
    File "/Library/Python/2.7/site-packages/pip-1.4.1-py2.7.egg/pip/util.py", line 294, in renames
      shutil.move(old, new)
    File "/usr/local/Cellar/python/2.7.9/Frameworks/Python.framework/Versions/2.7/lib/python2.7/shutil.py", line 300, in move
      rmtree(src)
    File "/usr/local/Cellar/python/2.7.9/Frameworks/Python.framework/Versions/2.7/lib/python2.7/shutil.py", line 247, in rmtree
      rmtree(fullname, ignore_errors, onerror)
    File "/usr/local/Cellar/python/2.7.9/Frameworks/Python.framework/Versions/2.7/lib/python2.7/shutil.py", line 252, in rmtree
      onerror(os.remove, fullname, sys.exc_info())
    File "/usr/local/Cellar/python/2.7.9/Frameworks/Python.framework/Versions/2.7/lib/python2.7/shutil.py", line 250, in rmtree
      os.remove(fullname)
  OSError: [Errno 13] Permission denied: '/Library/Python/2.7/site-packages/pip-1.4.1-py2.7.egg/EGG-INFO/dependency_links.txt'
  
  Storing complete log in /Users/[me]/.pip/pip.log
  </code></pre>
  
  <p>However, pip installs correctly to <code>/usr/local/lib/python2.7/site-packages</code> (the Homebrew-provided version), and I have no apparent issues with using pip to install modules and using the modules. Here's the output of <code>which</code>, after all of the above:</p>
  
  <pre><code>$ which pip
  /usr/local/bin/pip
  $ which python
  /usr/local/bin/python
  </code></pre>
  
  <p>What's going on? Any help would be appreciated.</p>