name : bad_chained_comparison.py # Licensed under the GPL: https://www.gnu.org/licenses/old-licenses/gpl-2.0.html # For details: https://github.com/PyCQA/pylint/blob/main/LICENSE # Copyright (c) https://github.com/PyCQA/pylint/blob/main/CONTRIBUTORS.txt from __future__ import annotations from typing import TYPE_CHECKING from astroid import nodes from pylint.checkers import BaseChecker from pylint.interfaces import HIGH if TYPE_CHECKING: from pylint.lint import PyLinter COMPARISON_OP = frozenset(("<", "<=", ">", ">=", "!=", "==")) IDENTITY_OP = frozenset(("is", "is not")) MEMBERSHIP_OP = frozenset(("in", "not in")) class BadChainedComparisonChecker(BaseChecker): """Checks for unintentional usage of chained comparison.""" name = "bad-chained-comparison" msgs = { "W3601": ( "Suspicious %s-part chained comparison using semantically incompatible operators (%s)", "bad-chained-comparison", "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).', ) } def _has_diff_semantic_groups(self, operators: list[str]) -> bool: # Check if comparison operators are in the same semantic group for semantic_group in (COMPARISON_OP, IDENTITY_OP, MEMBERSHIP_OP): if operators[0] in semantic_group: group = semantic_group return not all(o in group for o in operators) def visit_compare(self, node: nodes.Compare) -> None: operators = sorted({op[0] for op in node.ops}) if self._has_diff_semantic_groups(operators): num_parts = f"{len(node.ops)}" incompatibles = ( ", ".join(f"'{o}'" for o in operators[:-1]) + f" and '{operators[-1]}'" ) self.add_message( "bad-chained-comparison", node=node, args=(num_parts, incompatibles), confidence=HIGH, ) def register(linter: PyLinter) -> None: linter.register_checker(BadChainedComparisonChecker(linter))