What information exactly is `isnan` supposed to communicate? Put another way, given that it raises NotImplemented for unknown types, and that bool(NotImplemented) is True, is there a reason by it cannot return a Python bool (which seems more useful)? Thanks, Alan Isaac

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np.isnan(np.nan)

True

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np.isnan(np.nan) is True

False

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type(np.isnan(np.nan))

<type 'numpy.bool_'>

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np.isnan('')

NotImplemented

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bool(_)

True

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if np.isnan(''): print "Uh oh"

... Uh oh