runtime-import-in-type-checking-block (TCH004)

Derived from the flake8-type-checking linter.

Fix is sometimes available.

What it does

Checks for runtime imports defined in a type-checking block.

Why is this bad?

The type-checking block is not executed at runtime, so the import will not be available at runtime.

Example

from typing import TYPE_CHECKING

if TYPE_CHECKING:
    import foo


def bar() -> None:
    foo.bar()  # raises NameError: name 'foo' is not defined

Use instead:

import foo


def bar() -> None:
    foo.bar()

References

• PEP 535