title: PIP Installation doesn't work (six, numpy and python-dateutil requirements)
body: <p>I'm a quite new to Python and want to install the Pillow package on Mac for Python 3.5. I use the <code>pip install pillow</code>command and get this error:</p>
  
  <pre><code>Jaspers-MBP:~ jasperherrmann$ pip install pillow
  Collecting pillow
    Using cached Pillow-5.1.0-cp27-cp27m-macosx_10_6_intel.macosx_10_9_intel.macosx_10_9_x86_64.macosx_10_10_intel.macosx_10_10_x86_64.whl
  prompt-toolkit 1.0.15 has requirement six&gt;=1.9.0, but you'll have six 
  1.4.1 which is incompatible.
  pandas 0.22.0 has requirement numpy&gt;=1.9.0, but you'll have numpy 1.8.0rc1 which is incompatible.
  html5lib 1.0.1 has requirement six&gt;=1.9, but you'll have six 1.4.1 which is incompatible.
  matplotlib 1.3.1 has requirement numpy&gt;=1.5, but you'll have numpy 1.8.0rc1 which is incompatible.
  jupyter-client 5.2.3 has requirement python-dateutil&gt;=2.1, but you'll have python-dateutil 1.5 which is incompatible.
  Installing collected packages: pillow
  </code></pre>
  
  <p>So I go on and try to install all the things pandas, html5lib and so on seem to require with <code>pip install six</code>, <code>pip install numpy</code> and <code>pip install python-dateutil</code> and get the next error (for all commands the same):</p>
  
  <pre><code>Jaspers-MBP:~ jasperherrmann$ pip install six
  Requirement already satisfied: six in /System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python (1.4.1)
  prompt-toolkit 1.0.15 has requirement six&gt;=1.9.0, but you'll have six 1.4.1 which is incompatible.
  pandas 0.22.0 has requirement numpy&gt;=1.9.0, but you'll have numpy 1.8.0rc1 which is incompatible.
  html5lib 1.0.1 has requirement six&gt;=1.9, but you'll have six 1.4.1 which is incompatible.
  matplotlib 1.3.1 has requirement numpy&gt;=1.5, but you'll have numpy 1.8.0rc1 which is incompatible.
  jupyter-client 5.2.3 has requirement python-dateutil&gt;=2.1, but you'll have python-dateutil 1.5 which is incompatible.
  </code></pre>
  
  <p>So I thought all right six and the others are already there and I will just have to upgrade them with the <code>pip install --upgrade six</code> command. And this is were I get the last error and don't now how to continue:</p>
  
  <pre><code>Jaspers-MBP:~ jasperherrmann$ pip install --upgrade six
  Collecting six
    Using cached six-1.11.0-py2.py3-none-any.whl
  pandas 0.22.0 has requirement numpy&gt;=1.9.0, but you'll have numpy 1.8.0rc1 which is incompatible.
  matplotlib 1.3.1 has requirement numpy&gt;=1.5, but you'll have numpy 1.8.0rc1 which is incompatible.
  jupyter-client 5.2.3 has requirement python-dateutil&gt;=2.1, but you'll have python-dateutil 1.5 which is incompatible.
  Installing collected packages: six
    Found existing installation: six 1.4.1
  Cannot uninstall 'six'. It is a distutils installed project and thus we cannot accurately determine which files belong to it which would lead to only a partial uninstall.
  Jaspers-MBP:~ jasperherrmann$ 
  </code></pre>
  
  <p>So here I'm stuck and would be happy if some of you has a solution to my problem :-) </p>