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Description
It looks as though the datetime64 dtype breaks the Python rule that x == y should imply hash(x) == hash(y). This broke a Pandas application that was grouping on dates, and then doing a dictionary lookup to find the lines of a DataFrame associated to a particular date.
Python 3.3.2 (default, May 21 2013, 11:48:51)
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
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>>> import numpy
>>> numpy.__version__
'1.7.1'
>>> import datetime
>>> x = numpy.datetime64(datetime.datetime.now())
>>> y = numpy.datetime64(x, 'ns')
>>> x == y # gives the expected 'True'
True
>>> hash(x) == hash(y) # expected True
False