In a message of Wed, 14 Oct 2015 08:38:43 -0700, Guido van Rossum writes:
>Perhaps you could solve this with type variables. Here's a little
>demonstration program:
>```
>from decimal import Decimal
>from typing import TypeVar
>F = TypeVar('F', float, Decimal)
>def add(a: F, b: F) -> F:
> return a+b
>print(add(4.2, 3.14))
>print(add(Decimal('4.2'), Decimal('3.14')))
>print(add(Decimal('4.2'), 3.14))
>```
>Note that the last line is invalid. mypy correctly finds this:
>```
>flt.py:8: error: Type argument 1 of "add" has incompatible value "object"
>```
>(We could work on the error message.)
>
>Now, I'm not sure that this is the best solution given the audience -- but
>the type variable 'F' only needs to be defined once, so this might actually
>work.
>
>--
>--Guido van Rossum (python.org/~guido)
This looks good to me. I wonder if there is anything we can do,
documentation and PEP wise to encourage people who write code
to use it, rather than just using float?
Laura
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