title: pip was broken - pkg_resources.DistributionNotFound
body: <p>My environment is OSX High Sierra 10.13.6.</p>
  
  <pre><code>➜ python
  Python 3.7.2 (default, Jan 13 2019, 12:50:15)
  [Clang 10.0.0 (clang-1000.11.45.5)] on darwin
  
  ➜ python3
  Python 3.7.2 (default, Jan 13 2019, 12:50:15)
  [Clang 10.0.0 (clang-1000.11.45.5)] on darwin
  </code></pre>
  
  <p>If I entered pip, it throw error.</p>
  
  <pre><code>/usr/local/opt/python/libexec/bin/pip:6: UserWarning: Unbuilt egg for Unknown [unknown version] (/usr/local/lib/python3.7/site-packages)
    from pkg_resources import load_entry_point
  Traceback (most recent call last):
    File "/usr/local/lib/python3.7/site-packages/pkg_resources/__init__.py", line 581, in _build_master
      ws.require(__requires__)
    File "/usr/local/lib/python3.7/site-packages/pkg_resources/__init__.py", line 898, in require
      needed = self.resolve(parse_requirements(requirements))
    File "/usr/local/lib/python3.7/site-packages/pkg_resources/__init__.py", line 789, in resolve
      raise VersionConflict(dist, req).with_context(dependent_req)
  pkg_resources.VersionConflict: (pip 19.0.1 (/usr/local/lib/python3.7/site-packages), Requirement.parse('pip==18.1'))
  
  During handling of the above exception, another exception occurred:
  
  Traceback (most recent call last):
    File "/usr/local/opt/python/libexec/bin/pip", line 6, in &lt;module&gt;
      from pkg_resources import load_entry_point
    File "/usr/local/lib/python3.7/site-packages/pkg_resources/__init__.py", line 3126, in &lt;module&gt;
      @_call_aside
    File "/usr/local/lib/python3.7/site-packages/pkg_resources/__init__.py", line 3110, in _call_aside
      f(*args, **kwargs)
    File "/usr/local/lib/python3.7/site-packages/pkg_resources/__init__.py", line 3139, in _initialize_master_working_set
      working_set = WorkingSet._build_master()
    File "/usr/local/lib/python3.7/site-packages/pkg_resources/__init__.py", line 583, in _build_master
      return cls._build_from_requirements(__requires__)
    File "/usr/local/lib/python3.7/site-packages/pkg_resources/__init__.py", line 596, in _build_from_requirements
      dists = ws.resolve(reqs, Environment())
    File "/usr/local/lib/python3.7/site-packages/pkg_resources/__init__.py", line 784, in resolve
      raise DistributionNotFound(req, requirers)
  pkg_resources.DistributionNotFound: The 'pip==18.1' distribution was not found and is required by the application
  </code></pre>
  
  <p>I tried <code>pip install -U setuptools</code>, But it throw same error.</p>
  
  <p>Also re-installed with get-pip.py, it doesn't work.</p>
  
  <p>Maybe python path is twist in my system.</p>
  
  <p>How can I remove pip and python entirely and reinstalled?</p>
  
  <p>Thanks.</p>