ruff/crates/ty_python_semantic/resources/mdtest/narrow/hasattr.md

Narrowing using hasattr()

The builtin function hasattr() can be used to narrow nominal and structural types. This is accomplished using an intersection with a synthesized protocol:

from typing import final

class Foo: ...

@final
class Bar: ...

def f(x: Foo):
    if hasattr(x, "spam"):
        reveal_type(x)  # revealed: Foo & <Protocol with members 'spam'>
        reveal_type(x.spam)  # revealed: object

    if hasattr(x, "not-an-identifier"):
        reveal_type(x)  # revealed: Foo

def y(x: Bar):
    if hasattr(x, "spam"):
        reveal_type(x)  # revealed: Never
        reveal_type(x.spam)  # revealed: Never