Matplotlib depends on non-Python libraries.

On Linux and OSX, pkg-config_ can be used to find required non-Python

libraries and thus make the install go more smoothly if the libraries and

headers are not in the expected locations.

.. _pkg-config: https://www.freedesktop.org/wiki/Software/pkg-config/

If not using pkg-config (in particular on Windows), you may need to set the

include path (to the FreeType, libpng, and zlib headers) and link path (to

the FreeType, libpng, and zlib libraries) explicitly, if they are not in

standard locations. This can be done using standard environment variables

-- on Linux and OSX:

.. code-block:: sh

and on Windows:

.. code-block:: bat

where ``...`` means "also give, in the same format, the directories

containing ``png.h`` and ``zlib.h`` for the include path, and for

``libpng.so``/``png.lib`` and ``libz.so``/``z.lib`` for the link path."