[Numpy-discussion] Implementing hashing protocol for dtypes

Robert Kern robert.kern@gmail....
Wed Mar 11 15:36:22 CDT 2009


On Wed, Mar 11, 2009 at 15:06, David Cournapeau <cournape@gmail.com> wrote:
> Hi,
>
> I was looking at #936, to implement correctly the hashing protocol for
> dtypes. Am I right to believe that tp_hash should recursively descend
> fields for compound dtypes, and the hash value should depend on the
> size/ndim/typenum/byteorder for each "atomic" dtype + fields name (and
> titles) ? Contrary to comparison, we can't reuse the python C api,
> since PyObject_Hash cannot be applied to the fields dict, right ?

Usually, one constructs a hashable analogue; e.g. taking the .descr
and converting all of the lists to tuples. Then use PyObject_Hash on
that.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless
enigma that is made terrible by our own mad attempt to interpret it as
though it had an underlying truth."
  -- Umberto Eco


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