Remove redundant __nonzero__ methods From https://docs.python.org/2/reference/datamodel.html#specialnames : When this method is not defined, __len__() is called, if it is defined, and the object is considered true if its result is nonzero. Also helpful for an eventual migration to py3k, as __nonzero__ has been replaced with __bool__, which also defaults to looking at __len__ if undefined.

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