Pyright cannot detect condition context from property

[catcombo]

Hi folks!

Don't know if it's a bug or not. Here is the code example:

class Content:
    media_type: str


class ResponseView:
    def __init__(self, content: Content | None):
        self.content = content

    @property
    def has_content(self) -> bool:
        return self.content is not None

    @property
    def media_type(self) -> str | None:
        return self.content.media_type if self.has_content else None

pyright complains

But if I inline condition from has_content property then it stops complaining

Is it a bug? WDYT?

[erictraut]

Pyright is working as intended here, so this isn't a bug.

The has_content property is checking whether self.content is None, but this fact isn't visible outside of the has_content body. Static analysis tools like pyright, mypy, etc. do not propagate knowledge like this across function calls.

If you want your code to work with static analysis, you'll need to avoid this pattern. Here's one way that you could change your code to eliminate type errors:

    @property
    def media_type(self) -> str | None:
        # Check self.content directly rather than calling a method to check it
        return self.content.media_type if self.content else None

[catcombo]

Thanks for the detailed explanation, Eric!