flake8-future-annotations

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.

flake8 codes

Code	Description
FA100	Missing import if a type used in the module can be rewritten using PEP563
FA101	Missing import when no rewrite using PEP563 is available (see config)
FA102	Missing import when code uses simplified types (list, dict, set, etc)

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: FA100 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")

Configuration

If the --force-future-annotations option is set, missing from __future__ import annotations will be reported regardless of a rewrite available according to PEP 563; in this case, code FA101 is used instead of FA100.

If the --check-future-annotations option is set, missing from __future__ import annotations will be reported because the following code will error on Python versions older than 3.10 (this check does not output anything for versions 3.10+):

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

hello.py:1:1: FA102 Missing from __future__ import annotations but uses simplified type annotations: dict, list, union