Multiple assignments to _ with conflicting types in loops and comprehension results in error

[posita]

The following results in MyPy complaining Incompatible types in assignment (expression has type "unicode", variable has type "int"):

ints_n_txt = [(1, u'1'), (2, u'2'), (3, u'3')]  # type: List[Tuple[int, Text]]
for _, _ in ints_n_txt:  # _ has two different types
    pass

Unsurprisingly, this affects collection comprehension as well:

spam = [True for _, _ in ints_n_txt]  # type: List[bool]

Explicitly declaring the type of _ as Any "fixes" the error for the for loop:

_ = None  # type: Any
for _, _ in …

But that doesn't work for collection comprehension. (MyPy will still complain, and some linters will too. For example, flake8 will complain that F812 - list comprehension redefines '_' from line ….)

These seem to work, but both look a little awkward:

for (
            _,  # type: ignore
            _,  # type: ignore
        ) in ints_n_txt:
    pass

spam = [
    True for (
        _,  # type: ignore
        _,  # type: ignore
    ) in ints_n_txt
]  # type: List[bool]

This may be as intended. I'm wondering if treating _ in all scopes as type Any by default is a bad idea? (Apologies if this is more appropriately filed as an issue with typeshed.)

[ilevkivskyi]

Yes, this idea appeared before, so this is a duplicate of #465

[posita]

Oh jeez! Apologies for missing that! 😞

[ilevkivskyi]

No problem!