[Numpy-discussion] Re: dtype: hashing and cmp

[Robert Kern]

Simon Burton wrote:
> Is there a reason why dtype's are unhashable ? (ouch)

No one thought about it, probably. If you would like to submit a patch, I think
it we would check it in.

> On another point, is there a canonical list of dtype's ?
> I'd like to test the dtype of an array, and I always
> end up with something like this:
> 
> if array.dtype == numpy.dtype('l'): ...
> 
> When I would prefer to write something like:
> 
> if array.dtype == numpy.Int32: ...

numpy.int32

There is a list on page 20 of _The Guide to NumPy_. It is included in the sample
chapters:

  http://www.tramy.us/scipybooksample.pdf

> (i can never remember these char codes !)
> 
> Alternatively, should dtype's __cmp__ promote the other arg
> to a dtype before the compare ?
> I guess not, since that would break a lot of code: eg. dtype(None) 
> is legal.

Correct, it should not.

-- 
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