5-ary izip

[gnoack]

Obviously this is not the real solution, but it gets rid of the linter warning for now. :)

[matthiaskramm]

This is a syntax error - the "->" needs to be on the same line.

Also, would

@overload
def izip(*iter: Iterable) -> Iterator[tuple]: ...

do the trick?

[gnoack]

I believe that while that would work for n-ary calls, it would drop type information for the individual tuple positions, so spelling it out may be worth the tradeoff here and work in more cases. The use cases I've seen for izip are often of the form

for foo, bar in itertools.izip(foos, bars):
  frobnicate(foo, bar)

and it would make sense to keep the type information for foo and bar around.

[gvanrossum]

What lint error?

[matthiaskramm]

We use pytype as a linter, on our side. @gnoack is talking about the error you get when you do something like

import itertools
itertools.izip([], [], [], [], [])

[gnoack]

Ooh, I got it working. :) Up to what number of arguments should we go?

(I'm unfamiliar with the type specification language, I'm assuming that it doesn't technically work yet to both support n-ary arguments and still retain the types within the resulting tuples?)

[gvanrossum]

Thanks for the clarification. LGTM. I'll leave it to @matthiaskramm to merge.

[matthiaskramm]

Could you add the following:

def izip(*iter: Iterable) -> Iterator[tuple]

?

[matthiaskramm]

Oh, I see you already commented on that. Feel free to do the explicit version for as many arguments as you see fit, but the list of signatures should finish with the general case, even if it's less precise.

[gnoack]

Sounds good, adding 6-ary variant and n-ary fallback.

[gnoack]

Removed the fallback again, that didn't work in Python3.5 (see the more recent Travis failures).

[gnoack]

I had trouble adding the fallback case as you asked; It worked for the other two Python versions, but for Python3.5, Travis says:

stdlib/2/itertools.pyi:66: error: Overloaded function signatures 1 and 7 overlap with incompatible return types

I tried to make the return type Iterable[tuple], which should according to documentation be equivalent to Iterable[Tuple[Any, ...]], but it didn't work. I'm dropping the fallback again for now.

[JelleZijlstra]

The Python versions given in Travis are misleading; in fact "3.6" is flake8 (our linter), "3.5" is mypy, and "2.7" is pytype. I think it's a mypy bug that it rejects your last overload (the types are actually compatible), so feel free to file a bug against mypy.

[JelleZijlstra]

Merged, thanks! I hope nobody needs to izip seven iterables before we implement variadic type variables. :)

[sproshev]

I implemented the following fallback for builtin zip:

@overload
def zip(iter1: Iterable[Any], iter2: Iterable[Any], iter3: Iterable[Any],
        iter4: Iterable[Any], iter5: Iterable[Any], iter6: Iterable[Any],
        *iterables: Iterable[Any]) -> List[Tuple[Any, ...]]: ...

See #1041