Literal ellipsis and literal tuples

[joshbode]

I'm trying to determine how to annotate ellipsis (...) and I'm getting an error that ... is invalid for typing.Literal - is there a correct way to annotate a variable to indicate that it may contain ellipsis?

I also, out of curiosity, tried using a tuple as an element in Literal and got an unexpected result in that it appears the tuple is unpacked (e.g. Literal[("a", "b")] == Literal["a", "b"]) which may be correct, but surprised me :)

Inputs:

# test.py
from typing import Literal

x: Literal["a", 1, None, True, False]
y: Literal[("a", "b")]
z: Literal["a", ...]

x = "a"
y = ("a", "b")
z = ...

Output:

$ mypy test.py
test.py:5: error: Parameter 2 of Literal[...] is invalid
test.py:8: error: Incompatible types in assignment (expression has type "Tuple[str, str]", variable has type "Union[Literal['a'], Literal['b']]")
Found 2 errors in 1 file (checked 1 source file)

Versions:

$ python --version
Python 3.8.3
$ mypy --version
mypy 0.782

[JelleZijlstra]

From looking at typeshed, you should be able to annotate Ellipsis as ellipsis (https://github.com/python/typeshed/blob/master/stdlib/2and3/builtins.pyi#L1747). PEP 586 explicitly lists all types allowed as Literals (https://www.python.org/dev/peps/pep-0586/#legal-parameters-for-literal-at-type-check-time), and Ellipsis is not among them.

The tuple thing is because the AST is the same whether or not you put the parens in, so mypy can't (easily) distinguish between Literal[1, 2] and Literal[(1, 2)].

[JukkaL]

There seems to be no further action required.

[BvB93]

From looking at typeshed, you should be able to annotate Ellipsis as ellipsis

Based on, among others, #8240 there seems to be a desire to either make ellipsis private or get rid of it.
With this in mind I'm concerned that annotation objects using ellipsis will cause issues in the (near?) future.

[gvanrossum]

Based on, among others, #8240 there seems to be a desire to either make ellipsis private or get rid of it.
With this in mind I'm concerned that annotation objects using ellipsis will cause issues in the (near?) future.

You should probably petition the CPython project to add that type to types.py in the stdlib, so it can be added to typeshed.

[BvB93]

You should probably petition the CPython project to add that type to types.py in the stdlib, so it can be added to typeshed.

Yeah, that would be the most definitive solution; I just opened bpo-41810 for the (re-)introduction request.