title: Python packages hash not matching whilst installing using pip
body: <p>I am using pip to install all my python packages but get error as shown in the trace below. What is the problem and how can I solve it?</p>
  
  <pre><code>usr@comp:~$ pip install flask
      Collecting flask
        Using cached Flask-0.11.1-py2.py3-none-any.whl
      Collecting itsdangerous&gt;=0.21 (from flask)
        Using cached itsdangerous-0.24.tar.gz
      Collecting click&gt;=2.0 (from flask)
        Using cached click-6.6.tar.gz
      Collecting Werkzeug&gt;=0.7 (from flask)
        Using cached Werkzeug-0.11.11-py2.py3-none-any.whl
      Requirement already satisfied (use --upgrade to upgrade): Jinja2&gt;=2.4 in /usr/lib/python2.7/dist-packages (from flask)
      Requirement already satisfied (use --upgrade to upgrade): MarkupSafe in /usr/lib/python2.7/dist-packages (from Jinja2&gt;=2.4-&gt;flask)
      THESE PACKAGES DO NOT MATCH THE HASHES FROM THE REQUIREMENTS FILE. If you have updated the package versions, please update the hashes. Otherwise, examine the package contents carefully; someone may have tampered with them.
          Werkzeug&gt;=0.7 from https://pypi.python.org/packages/a9/5e/41f791a3f380ec50f2c4c3ef1399d9ffce6b4fe9a7f305222f014cf4fe83/Werkzeug-0.11.11-py2.py3-none-any.whl#md5=c63a21eedce9504d223ed89358c4bdc9 (from flask):
          Expected md5 c63a21eedce9504d223ed89358c4bdc9
               Got        13a168aafcc43354b6c79ef44bb0dc71
  </code></pre>