pylab/networkx; no node labels displayed after update
This is hitting a known (but unresolved) bug in the OSX backend (#3470).
Switching to one of the Agg based backends should 'resolve' the problem by avoiding it.
UPDATE
Part of the problem has been identified and merged https://github.com/matplotlib/matplotlib/pull/3564. This fix should be in mpl v1.4.1 and higher.