title: pip uninstall working but giving error
body: <p>I have downloaded, built and installed the sample pypi project. The project is supposed to be used to give an insight to python packaging and is referenced in <a href="https://packaging.python.org/en/latest/" rel="noreferrer">Python Packaging User Guide</a> and <a href="https://packaging.python.org/en/latest/distributing/" rel="noreferrer">Packaging and Distributing Projects</a>. I am therefore confused to why on earth following their instructions on creating the package I have an error when uninstalling it.</p>
  
  <p>As mentioned above I have used their sample project. If anyone can shed some light it would be appreciated. </p>
  
  <p>Key notes: I am running Mac OSX, my installed python version is 3.5.1
  Below are steps to reproduce the problem:</p>
  
  <pre><code>mkdir testdirectory 
  cd testdirectory/
  pyvenv venv    # Creating a virtual environment
  source venv/bin/activate
  git clone https://github.com/pypa/sampleproject.git    # Getting sample project
  cd sampleproject/
  python setup.py build
  python setup.py install    # Installing on the virtual environment
  
  pip list
  peppercorn (0.5)
  pip (7.1.2)
  sample (1.2.0)
  setuptools (18.2)
  
  pip uninstall sample
  </code></pre>
  
  <p>Resulting in the following output:</p>
  
  <pre><code>Uninstalling sample-1.2.0:
    /Users/steve/testdirectory/venv/bin/sample
    /Users/steve/testdirectory/venv/lib/python3.5/site-packages/sample-1.2.0-py3.5.egg
  Proceed (y/n)? y
    Successfully uninstalled sample-1.2.0
  Traceback (most recent call last):
    File "/Users/steve/testdirectory/venv/bin/pip3", line 11, in &lt;module&gt;
      sys.exit(main())
    File "/Users/steve/testdirectory/venv/lib/python3.5/site-packages/pip/__init__.py", line 217, in main
      return command.main(cmd_args)
    File "/Users/steve/testdirectory/venv/lib/python3.5/site-packages/pip/basecommand.py", line 248, in main
      pip_version_check(session)
    File "/Users/steve/testdirectory/venv/lib/python3.5/site-packages/pip/utils/outdated.py", line 102, in pip_version_check
      installed_version = get_installed_version("pip")
    File "/Users/steve/testdirectory/venv/lib/python3.5/site-packages/pip/utils/__init__.py", line 858, in get_installed_version
      working_set = pkg_resources.WorkingSet()
    File "/Users/steve/testdirectory/venv/lib/python3.5/site-packages/pip/_vendor/pkg_resources/__init__.py", line 629, in __init__
      self.add_entry(entry)
    File "/Users/steve/testdirectory/venv/lib/python3.5/site-packages/pip/_vendor/pkg_resources/__init__.py", line 685, in add_entry
      for dist in find_distributions(entry, True):
    File "/Users/steve/testdirectory/venv/lib/python3.5/site-packages/pip/_vendor/pkg_resources/__init__.py", line 2075, in find_eggs_in_zip
      if metadata.has_metadata('PKG-INFO'):
    File "/Users/steve/testdirectory/venv/lib/python3.5/site-packages/pip/_vendor/pkg_resources/__init__.py", line 1605, in has_metadata
      return self.egg_info and self._has(self._fn(self.egg_info, name))
    File "/Users/steve/testdirectory/venv/lib/python3.5/site-packages/pip/_vendor/pkg_resources/__init__.py", line 1963, in _has
      return zip_path in self.zipinfo or zip_path in self._index()
    File "/Users/steve/testdirectory/venv/lib/python3.5/site-packages/pip/_vendor/pkg_resources/__init__.py", line 1843, in zipinfo
      return self._zip_manifests.load(self.loader.archive)
    File "/Users/steve/testdirectory/venv/lib/python3.5/site-packages/pip/_vendor/pkg_resources/__init__.py", line 1783, in load
      mtime = os.stat(path).st_mtime
  FileNotFoundError: [Errno 2] No such file or directory: '/Users/steve/testdirectory/venv/lib/python3.5/site-packages/sample-1.2.0-py3.5.egg'
  </code></pre>
  
  <p>It appears that the package has uninstalled correctly however the error is still thrown.</p>