`x = tuple() # type: Tuple[()]` Incompatible types in assignment

[asottile]

I understand this is a silly example, but figured I'd report it anyway.

I can't find a way (other than # type: ignore) to silence mypy for this line:

x = tuple()  # type: Tuple[()]

I found #4211 (which is how I got to Tuple[()]

mypy 0.660 errors with:

testing/resources/builtin_constructors.py:13: error: Incompatible types in assignment (expression has type "Tuple[<nothing>, ...]", variable has type "Tuple[]")

[gvanrossum]

I don't think this is a bug. Every tuple call returns a Tuple[T, ...] for some T, which is not the same as an empty tuple -- it is a tuple containing an arbitrary number of Ts.

Unless you have an actual use case I don't think we should try to special-case calling tuple() without arguments. (It's a class constructor, not a function, so you can't use standard overload syntax to say it returns an empty tuple when called without arguments.)

[ilevkivskyi]

At some point mypy might support honoring the return type of __new__(), see #1020, so that we will be able to add an overload for empty tuple. We can probably keep this open as a low priority feature.

[JelleZijlstra]

x = () # type: Tuple[()] works fine. I don't think this is worth any special casing in mypy. We're discussing adding a special case in typeshed instead, though I'm skeptical about that too.