This rule raises an issue when a TypeVar is used in a function instead of the generic function type syntax.

Why is this an issue?

Prior to Python 3.12 functions using generic types were created as follows:

from typing import TypeVar

_T = TypeVar("_T")

def func(a: _T, b: _T) -> _T:
    ...

This snippet of code can be confusing and difficult to read. This is why is it a good idea to use the new type parameter syntax of Python 3.12 that allows for a more concise and more readable code by removing the TypeVar and its import statement:

def func[T](a: T, b: T) -> T:
    ...

Exceptions

This rule will only raise an issue when the Python version of the analyzed project is set to 3.12 or higher.

How to fix it

To fix this issue, replace the usage of a TypeVar as a parameter type with the generic type parameter syntax.

Code examples

Noncompliant code example

from typing import TypeVar

_T = TypeVar("_T", bound=str)

def func(a: _T, b: int) -> _T: # Noncompliant: the usage of a TypeVar could be simplified with a generic type parameter.
    ...

Compliant solution

def func[T: str](a: T, b: int) -> T: # Compliant: the code is clear and concise.
    ...

Resources

Documentation