[Python-Dev] PEP 0484 - the Numeric Tower (original) (raw)

Laura Creighton lac at openend.se
Wed Oct 14 16:56:22 EDT 2015

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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