set operations and unpacking

[Molkree]

Bug Report

Error on a valid code.

To Reproduce

sets = map(set[str], ["aaa", "abb", "acc"])
intersection = set[str].intersection(*sets)

mypy Playground

Actual Behavior

Argument 1 to "intersection" of "set" has incompatible type "*map[Set[str]]"; expected "Set[_T]" [arg-type]

Your Environment

• Mypy version used: 0.991
• Mypy command-line flags: --strict (it's present without strict checking as well)
• Mypy configuration options from mypy.ini (and other config files): None
• Python version used: 3.11

This issue is present for a bunch of other set methods like union and difference (I guess all of them that accept *s: Iterable[T]).
Possibly related #9706.

[Kein]

Same:

@dataclass
class StatsEntry:
    val0: int
    val1: int
    val2: int

    def __post_init__(self) -> None:
        for field in dcfields(self):
            value = getattr(self, field.name)
            setattr(self, field.name, field.type(value))


entry = line.rstrip().split(',')
stat = StatsEntry(*entry) #type: ignore
# Argument 1 to "StatsEntry" has incompatible type "*List[str]"; expected "int"  [arg-type]mypy(error)

[randolf-scholz]

Another example (mypy-playground):

from typing import Mapping, Any

def joint_keys(*dicts: Mapping[str, Any]) -> set[str]:
    """Find joint keys in collection of dictionaries."""
    return set.intersection(*map(set, dicts))    # ✘ [arg-type]

def joint_keys2(*dicts: Mapping[str, Any]) -> set[str]:
    """Find joint keys in collection of dictionaries."""
    dicts_keys: map[set[str]] = map(set, dicts)  # ✔
    return set.intersection(*dicts_keys)         # ✔

pyright raises no errors, so likely an issue with mypy (and not with stubs).

EDIT: It is fixed using the --new-type-inference flag on master branch

https://mypy-play.net/?mypy=master&python=3.11&gist=95765a01a9543509a1c740f4f9448397&flags=new-type-inference

[Molkree]

@randolf-scholz your example raises no errors since mypy 1.7 (released Nov 10, 2023) where new type inference was enabled by default.

My original repro raises no errors since mypy 1.14 (released Dec 19, 2024).

[Molkree]

Original repro raises an error once again in mypy 1.14.1

Reason is, mypy stopped raising in 1.14.0 due to a bug (inferring Any instead of a more precise type).

So this issue wasn't really fixed, reopening.