I installed matplotlib 2.0 the other day via

sudo -H pip install -U matplotlib

and found that, for the simplest of examples,

import matplotlib.pyplot as plt
plt.plot([1,2,3,4])
plt.ylabel('some numbers')
plt.show()

no plot would be produced. Upon setting the backend in /usr/local/lib/python2.7/dist-packages/matplotlib/mpl-data/m‌​atplotlibrc to TkAgg, it all worked again, and in fact TkAgg turned out to be the only backend to produce a plot at all.

Any hints on how to debug this?