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unnecessary-default-type-args (UP043)

Added in 0.8.0 · Related issues · View source

Derived from the pyupgrade linter.

Fix is always available.

What it does

Checks for unnecessary default type arguments for Generator and AsyncGenerator on Python 3.13+. In preview, this rule will also apply to stub files.

Why is this bad?

Python 3.13 introduced the ability for type parameters to specify default values. Following this change, several standard-library classes were updated to add default values for some of their type parameters. For example, Generator[int] is now equivalent to Generator[int, None, None], as the second and third type parameters of Generator now default to None.

Omitting type arguments that match the default values can make the code more concise and easier to read.

Example

from collections.abc import Generator, AsyncGenerator


def sync_gen() -> Generator[int, None, None]:
    yield 42


async def async_gen() -> AsyncGenerator[int, None]:
    yield 42

Use instead:

from collections.abc import Generator, AsyncGenerator


def sync_gen() -> Generator[int]:
    yield 42


async def async_gen() -> AsyncGenerator[int]:
    yield 42

Fix safety

This rule's fix is marked as safe, unless the type annotation contains comments.

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References