How to define overloaded type signatures?

Question

I have a Python function with an overloaded signature, for example float → float, str → int. I would like it to have it typed correctly, using annotations etc., so that mypy can check it correctly, and that tools like autocomplete will work. Is this possible? I appreciate different tools will have varying support, so mypy can be the standard for this question. I can use any released version of Python 3.

Answer 1

Yes, you can use the @typing.overload decorator.

From https://docs.python.org/3/library/typing.html#typing.overload:

@overload
def process(response: None) -> None:
    ...
@overload
def process(response: int) -> tuple[int, str]:
    ...
@overload
def process(response: bytes) -> str:
    ...
def process(response):
    <actual implementation>

Those ellipses (...) are literal. You will actually type three dots for each overloaded function signature. The actual code will go in the final definition.