Bug Report

mypy warns about the right side of a condition being unreachable when a variable is reset in an outer loop, then set again inside the inner loop.

To Reproduce

from typing import Optional

test: Optional[float] = None
reveal_type(test)  # Revealed type: Union[builtins.float, None]

for i in range(10):
    test = None
    reveal_type(test)  # Revealed type: None (???)
    for k in range(10):
        if test is None or k > test:
           test = k

Expected Behavior

No error.

Actual Behavior

mypy outputs error: Right operand of "or" is never evaluated. This is clearly because the type of test is re-evaluated at some point, even though it was declared with a type and no statement narrows that type.

This appears related to #7204, #8721, #8865, #13973, #14120, except it can't be solved by declaring the type of the variable before the loop in which it's updated (because that violates no-redef).

Note: I'm not sure why anyone would want to actually do this in practice. But I thought it might provide a useful test case.

Your Environment

• Mypy version used: 1.1.1
• Mypy command-line flags: --disable-error-code name-defined, plus a few others that I don't believe could possibly have any relevance.
• Mypy configuration options from mypy.ini (and other config files): None
• Python version used: 3.10.10