Using matplotlib 1.5.1 with Enthought Canopy (python 2.7.10 and ipython 4.1.2), if I run ipython --gui=qt and then import matplotlib.pyplot as plt the following exception is raised despite both PySide and PyQt4 being installed.

ImportError: Matplotlib qt-based backends require an external PyQt4, PyQt5,
or PySide package to be installed, but it was not found.

This happens with matplotlibrc backend.qt4 : PySide but not backend.qt4 : PyQt4.