[Python-Dev] PEP 0484 - the Numeric Tower

[Laura Creighton]

In a message of Wed, 14 Oct 2015 23:49:33 +0100, Oscar Benjamin writes:
>I'm sure the bokeh developers will be aware of the different ways that
>their library is used (at this level). If the input spec is "sequence of
>coercible to float" then I agree that they should use type annotations to
>match that rather than putting float and I imagine they would welcome your
>PR.
>
>Guido's suggestion is not general enough for that though: what about
>Fraction, mpf, gmpy, numpy, sympy, h5py etc? The ABCs in the numeric tower
>are unused by 3rd party types making them useless for abstract type
>inference (IMO). AFAIK the lowest common denominator among number types in
>Python is the __float__ special method. Does mypy have a way to require (a
>sequence of) that?

Thank you Oscar, and Chris Barker, and Guido for improving my thoughts
on this matter.  I go to bed now, pondering the idea that for me, internally,
a new way to do type annotation  'to-x-or-is-coercible-to-x' seems
a decent-enough idea.  Seems a betrayal of earlier principles.  Perhaps
when I wake up I will feel differently.  Off to dream about 'the
meaning of type annotation' then. :)  Thank you.

Laura