On Sat, Nov 28, 2020 at 10:02 AM Abdulla Al Kathiri < alkathiri.abdu...@gmail.com> wrote:
> Initially, when I wrote this, I had a similar syntax to what you wrote. I > like it, I changed it to brackets so we could contain Callable that has > multiple arguments or return value as Callables themselves. > > E.g., function that has two Callables as arguments and a Callable return > looks like this.. > > f: ((int, str) -> int, (…) -> str) -> (str) -> int > > The arguments are clear to me but the callable return confuses me a little > (the last two ->’s). However, the return value does’t have parenthesis, I > still could see the consistency (arguments) -> return. But my mind is > focusing on the last item, int, instead of the whole (str) -> int for some > reason. > You could parenthesize the return value if you think it's not clear. (IIRC some functional languages like Haskell use the ... -> ... -> ... notation to indicate functions of multiple arguments, so it's probably good to avoid looking like that -- even if it'sconsistent it would mislead people into thinking that Python uses a similar idiom. > > [[int, str -> int], [… -> str] -> [str -> int]] looks uglier but the one > before last “->" clearly communicates that the return value is callable. > > > Regardless of how it’s done, the less we depend on the typing module for > annotations, the better I think because it encourages python users to > annotate their functions. > Indeed. Shantanu did some quick counting and found that after 'Any' and the types covered by PEP 585, Callable is by far the most used: https://bugs.python.org/issue42102#msg381155 -- --Guido van Rossum (python.org/~guido) *Pronouns: he/him **(why is my pronoun here?)* <http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>
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