bad-chained-comparison / W3601

Message emitted:

Suspicious %s-part chained comparison using semantically incompatible operators (%s)

Description:

Used when there is a chained comparison where one expression is part of two comparisons that belong to different semantic groups ("<" does not mean the same thing as "is", chaining them in "0 < x is None" is probably a mistake).

Problematic code:

parrot.py:

shop = {
    # animal: (specie, descriptions)
    "parrot": ("Norvegian blue", ("restin'", "remarkable", "beautiful plumage")),
}

if "parrot" in shop is "restin'":  # [bad-chained-comparison]
    print("Hellooooo, Pooolllllyyy ! WAAAAKEEY, WAKKEEEY !")

xor.py:

def xor_check(*, left=None, right=None):
    if left is None != right is None:  # [bad-chained-comparison]
        raise ValueError(
            "Either both left= and right= need to be provided or none should."
        )

Correct code:

parrot.py:

shop = {
    # animal: (specie, descriptions)
    "parrot": ("Norvegian blue", ("restin'", "remarkable", "beautiful plumage")),
}

if "parrot" in shop and "restin'" in shop["parrot"][1]:
    print("Hellooooo, Pooolllllyyy ! WAAAAKEEY, WAKKEEEY !")

xor.py:

def xor_check(*, left=None, right=None):
    if (left is None) != (right is None):
        raise ValueError(
            "Either both left= and right= need to be provided or none should."
        )

Related links:

• Comparison Chaining

Created by the bad-chained-comparison checker.