flake8-future-annotations

Verifies python 3.7+ files use from __future__ import annotations if a type is used in the module that can be rewritten using PEP 563.

Pairs well with pyupgrade with the --py37-plus flag or higher, since pyupgrade only replaces type annotations with the PEP 563 rules if from __future__ import annotations is present.

For example:

import typing as t
from typing import List

def function(a_dict: t.Dict[str, t.Optional[int]]) -> None:
    a_list: List[str] = []
    a_list.append("hello")

As a result, this plugin will emit:

hello.py:1:1: F Missing from __future__ import annotations but imports: List, t.Dict, t.Optional

After adding the future annotations import, running pyupgrade allows the code to be automatically rewritten as:

from __future__ import annotations

def function(a_dict: dict[str, int | None]) -> None:
    a_list: list[str] = []
    a_list.append("hello")