Method dangerous_comparison

mypy/checkexpr.py:3847–3976

Check for dangerous non-overlapping comparisons like 42 == 'no'. The original_container is the original container type for 'in' checks (and None for equality checks). Rules: * X and None are overlapping even in strict-optional mode. This is to allow

(
        self,
        left: Type,
        right: Type,
        *,
        original_container: Type | None = None,
        seen_types: set[tuple[Type, Type]] | None = None,
        prefer_literal: bool = True,
        identity_check: bool = False,
    )

        return None

    def dangerous_comparison(
        self,
        left: Type,
        right: Type,
        *,
        original_container: Type | None = None,
        seen_types: set[tuple[Type, Type]] | None = None,
        prefer_literal: bool = True,
        identity_check: bool = False,
    ) -> bool:
        """Check for dangerous non-overlapping comparisons like 42 == 'no'.

        The original_container is the original container type for 'in' checks
        (and None for equality checks).

        Rules:
            * X and None are overlapping even in strict-optional mode. This is to allow
            'assert x is not None' for x defined as 'x = None  # type: str' in class body
            (otherwise mypy itself would have couple dozen errors because of this).
            * Optional[X] and Optional[Y] are non-overlapping if X and Y are
            non-overlapping, although technically None is overlap, it is most
            likely an error.
            * Any overlaps with everything, i.e. always safe.
            * Special case: b'abc' in b'cde' is safe.
        """
        if not self.chk.options.strict_equality:
            return False

        if seen_types is None:
            seen_types = set()
        if (left, right) in seen_types:
            return False
        seen_types.add((left, right))

        left, right = get_proper_types((left, right))

        # We suppress the error for equality and container checks if there is a custom __eq__()
        # method on either side. User defined (or even standard library) classes can define this
        # to return True for comparisons between non-overlapping types.
        if (
            custom_special_method(left, "__eq__") or custom_special_method(right, "__eq__")
        ) and not identity_check:
            return False

        if prefer_literal:
            # Also flag non-overlapping literals in situations like:
            #    x: Literal['a', 'b']
            #    if x == 'c':
            #        ...
            left = try_getting_literal(left)
            right = try_getting_literal(right)

        if self.chk.binder.is_unreachable_warning_suppressed():
            # We are inside a function that contains type variables with value restrictions in
            # its signature. In this case we just suppress all strict-equality checks to avoid
            # false positives for code like:
            #
            #     T = TypeVar('T', str, int)