Ubuntu running `pip install` gives error 'The following required packages can not be built: * freetype'

When performing pip install -r requirements.txt, I get the following error during the stage where it is installing matplotlib:

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.]

...

The following required packages can not be built:

                    * freetype

Shouldn't pip install -r requirements.txt also install freetype? How should freetype be installed in Ubuntu 12.04 so it works with matplotlib?

No. pip will not install system-level dependencies. This means pip will not install RPM(s) (Redhat based systems) or DEB(s) (Debian based systems).

To install system dependencies you will need to use one of the following methods depending on your system.

Ubuntu/Debian:

apt-get install libfreetype6-dev

To search for packages on Ubuntu/Debian based systems:

apt-cache search <string>

e.g:

apt-cache search freetype | grep dev

Redhat/CentOS/Fedora:

yum -y install freetype-devel

To search for packages on Redhat/CentOS/Fedora based systems:

yum search <string>

e.g:

yum search freetype | grep devel

Mac OS X: (via Homebrew)

brew install freetype

To search for packages on Mac OS X based systems:

brew search <string>

e.g:

brew search freetype

I had to install libxft-dev in order to enable matplotlib on ubuntu server 14.04.

sudo apt-get install libfreetype6-dev libxft-dev

And then I could use

sudo easy_install matplotlib