matplotlib/matplotlib — pull request #2128 by sinhrks (2013-06-17 11:37:55+00:00)
Title: figure.legend can be called without arguments

figure.legend() can be called without arguments.

In this case, figure legend artists will be created from all the contained axes legend handles and labels in the figure. The figure legend will merge handles if its label is identical, assuming that the same handlers is assigned to the same label names in subplots.