UserWarning: Matplotlib is building the font cache using fc-list. This may take a moment

Most probably matplotlib 1.5.1 have installed in your machine and you may experience to get this kind of warning:

/usr/lib/python2.7/dist-packages/matplotlib/font_manager.py:273: UserWarning: Matplotlib is building the font cache using fc-list. This may take a moment.
  warnings.warn('Matplotlib is building the font cache using fc-list. This may take a moment.')

To rid off from this warning please upgrade matplotlib by:

*sudo pip install --upgrade matplotlib*