set operations and unpacking

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.

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)

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

@randolf-scholz

@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).

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.

Use checkmember.py to check protocol subtyping (python#18943)

Navigation Menu

Repository navigation

`set` operations and unpacking #14259

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

set operations and unpacking #14259

Description

Activity

Kein commented on Jan 19, 2023

randolf-scholz commented on Aug 3, 2023

Molkree commented on Dec 22, 2024

Molkree commented on Jan 5, 2025

Metadata

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

Issue actions

`set` operations and unpacking #14259