title: Ubuntu running `pip install` gives error 'The following required packages can not be built: * freetype'
body: <p>When performing <code>pip install -r requirements.txt</code>, I get the following error during the stage where it is installing <code>matplotlib</code>:</p>
  
  <pre><code>REQUIRED DEPENDENCIES AND EXTENSIONS
                   numpy: yes [not found. pip may install it below.]
                dateutil: yes [dateutil was not found. It is required for date
                          axis support. pip/easy_install may attempt to
                          install it after matplotlib.]
                 tornado: yes [tornado was not found. It is required for the
                          WebAgg backend. pip/easy_install may attempt to
                          install it after matplotlib.]
               pyparsing: yes [pyparsing was not found. It is required for
                          mathtext support. pip/easy_install may attempt to
                          install it after matplotlib.]
                   pycxx: yes [Couldn't import.  Using local copy.]
                  libagg: yes [pkg-config information for 'libagg' could not
                          be found. Using local copy.]
                freetype: no  [pkg-config information for 'freetype2' could
                          not be found.]
  </code></pre>
  
  <p>...</p>
  
  <pre><code>The following required packages can not be built:
  
                      * freetype
  </code></pre>
  
  <p>Shouldn't <code>pip install -r requirements.txt</code> also install freetype? How should freetype be installed in Ubuntu 12.04 so it works with <code>matplotlib</code>?</p>