title: python - pip is not working after upgrade
body: <p>I tried upgrade pip3 with this command:</p>
  
  <blockquote>
    <p>sudo pip3 install --upgrade pip</p>
  </blockquote>
  
  <p>but unfortunately it doesn't work anymore and shows this message:</p>
  
  <blockquote>
    <p>pip3 --version</p>
  </blockquote>
  
  <p>message:</p>
  
  <blockquote>
    <p>Traceback (most recent call last):<br>
    File
    "/usr/local/lib/python3.4/dist-packages/pkg_resources/<strong>init</strong>.py",
    line 651, in _build_master
        ws.require(<strong>requires</strong>)<br>
    File "/usr/local/lib/python3.4/dist-packages/pkg_resources/<strong>init</strong>.py",
    line 952, in require
        needed = self.resolve(parse_requirements(requirements))<br>
    File "/usr/local/lib/python3.4/dist-packages/pkg_resources/<strong>init</strong>.py",
    line 844, in resolve
        raise VersionConflict(dist, req).with_context(dependent_req) pkg_resources.VersionConflict: (pip 7.1.2
    (/usr/local/lib/python3.4/dist-packages),
    Requirement.parse('pip==1.5.6'))</p>
    
    <p>During handling of the above exception, another exception occurred:</p>
    
    <p>Traceback (most recent call last):<br>
    File "/usr/local/bin/pip3", line 5, in 
        from pkg_resources import load_entry_point<br>
    File "/usr/local/lib/python3.4/dist-packages/pkg_resources/<strong>init</strong>.py", line 3084, in 
        @_call_aside<br>
    File "/usr/local/lib/python3.4/dist-packages/pkg_resources/<strong>init</strong>.py", line 3070, in _call_aside
        f(*args, **kwargs)<br>
    File "/usr/local/lib/python3.4/dist-packages/pkg_resources/<strong>init</strong>.py", line 3097, in _initialize_master_working_set
        working_set = WorkingSet._build_master()<br>
    File "/usr/local/lib/python3.4/dist-packages/pkg_resources/<strong>init</strong>.py", line 653, in _build_master
        return cls._build_from_requirements(<strong>requires</strong>)<br>
    File "/usr/local/lib/python3.4/dist-packages/pkg_resources/<strong>init</strong>.py", line 666, in _build_from_requirements
        dists = ws.resolve(reqs, Environment())<br>
    File "/usr/local/lib/python3.4/dist-packages/pkg_resources/<strong>init</strong>.py", line 839, in resolve
        raise DistributionNotFound(req, requirers) pkg_resources.DistributionNotFound: The 'pip==1.5.6' distribution was
    not found and is required by the application</p>
  </blockquote>
  
  <p>How to fix it?</p>