[Python-ideas] Variable-length, homogeneous tuple: why? (was: Optional static typing -- the crossroads)

[Guido van Rossum]

I still think you are mistaken. I don't think mypy has a way to spell a
homogeneous arbitrary-length tuple. All uses of Tuple[...] refer to
"anonymous struct" tuples.

I tried this:

from typing import Tuple

def f(a: Tuple[int]) -> None:
    pass

def main() -> None:
    f((1,))
    f((1, 2))

and I get an error for the second call, f((1, 2)):

a.py: In function "main":
a.py, line 8: Argument 1 to "f" has incompatible type "Tuple[int, int]";
expected "Tuple[int]"



On Sun, Aug 17, 2014 at 3:46 PM, Andrew Barnert <
abarnert at yahoo.com.dmarc.invalid> wrote:

> On Sunday, August 17, 2014 1:34 PM, Guido van Rossum <guido at python.org>
> wrote:
>
> >Where is it said that Tuple[int] is a homogeneous variable size list?
>
>
> (I'm assuming you're referring to the homogeneity and arbitrary length
> here, not the fact that someone presumably said "list" when they meant
> "tuple", because otherwise the answer is trivial…)
>
> First, that's how the current typing.py interprets it: Tuple[str] is a
> homogeneous, arbitrary-length (although of course unchanging, because it's
> immutable) tuple of strings.
>
>
> Second, what else _would_ it mean? If List[str] and Set[str] mean
> homogeneous arbitrary-length lists and sets of strs, and the same goes for
> Iterable[str] and MutableSequence[str] and IO[str] and AnyStr[str] and
> every other example in typing.py, it would be pretty surprising if it
> weren't the same for Tuple[str].
>
> Third, if it didn't mean that, how would you define the argument types to
> any of Nick's examples? For example:
>
>     def isinstance(obj: object, types: type | Tuple[type]) -> bool:
>
> That had better mean a homogeneous arbitrary-length tuple of types; if
> not, there doesn't seem to be any other way to declare its type.
>



-- 
--Guido van Rossum (python.org/~guido)
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