"inline" instruction inside docstring/comments

[gantsevdenis]

Current behavior is following:

from typing import Optional


def is_not_none(x)-> bool:
    """
    mypy:inline
    """
    return x is not None  # mypy:inline


# sample.py:16: error: Unsupported left operand type for + ("None")
# sample.py:16: note: Left operand is of type "Optional[str]"

def being_tested(x: Optional[str]) -> str:
    if is_not_none(x):
        return x + "a"
    return ""

The variable "x" can't be None, because the check is performed outside.

I don't know how difficult it would be to retrieve the instruction "inline" inside the docstring, and perform on-the fly inlining of the function body, whenever it is encountered. I
The "inline" instruction can be in comments.
So here the modified version would look like:

def being_tested(x: Optional[str]) -> str:
    if (x is not None):
        return x + "a"
    return ""

Only one-liners would be candidates for inlining, the first and the only expression after the return statement.
This would solve the false error above.
I am not sure however how line numbers would be handled, when reporting in the console.

Does this suggestion even makes sens?

[ilevkivskyi]

I think a decorator like @inline would be a better syntax. Anyway, I think this may be tricky and I rather prefer better support for literal types + NoReturn, see e.g. #5206 and #4063

[hauntsaninja]

PEP 647 can also do things like this