# 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 """Checks for yoda comparisons (variable before constant) See https://en.wikipedia.org/wiki/Yoda_conditions. """ from __future__ import annotations from typing import TYPE_CHECKING from astroid import nodes from pylint.checkers import BaseChecker, utils if TYPE_CHECKING: from pylint.lint import PyLinter REVERSED_COMPS = {"<": ">", "<=": ">=", ">": "<", ">=": "<="} COMPARISON_OPERATORS = frozenset(("==", "!=", "<", ">", "<=", ">=")) class MisplacedComparisonConstantChecker(BaseChecker): """Checks the placement of constants in comparisons.""" # configuration section name name = "comparison-placement" msgs = { "C2201": ( "Comparison should be %s", "misplaced-comparison-constant", "Used when the constant is placed on the left side " "of a comparison. It is usually clearer in intent to " "place it in the right hand side of the comparison.", {"old_names": [("C0122", "old-misplaced-comparison-constant")]}, ) } options = () def _check_misplaced_constant( self, node: nodes.Compare, left: nodes.NodeNG, right: nodes.NodeNG, operator: str, ) -> None: if isinstance(right, nodes.Const): return operator = REVERSED_COMPS.get(operator, operator) suggestion = f"{right.as_string()} {operator} {left.value!r}" self.add_message("misplaced-comparison-constant", node=node, args=(suggestion,)) @utils.only_required_for_messages("misplaced-comparison-constant") def visit_compare(self, node: nodes.Compare) -> None: # NOTE: this checker only works with binary comparisons like 'x == 42' # but not 'x == y == 42' if len(node.ops) != 1: return left = node.left operator, right = node.ops[0] if operator in COMPARISON_OPERATORS and isinstance(left, nodes.Const): self._check_misplaced_constant(node, left, right, operator) def register(linter: PyLinter) -> None: linter.register_checker(MisplacedComparisonConstantChecker(linter))