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- # 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
- """
- Checks for yoda comparisons (variable before constant)
- See https://en.wikipedia.org/wiki/Yoda_conditions
- """
- from astroid import nodes
- from pylint.checkers import BaseChecker, utils
- from pylint.interfaces import IAstroidChecker
- REVERSED_COMPS = {"<": ">", "<=": ">=", ">": "<", ">=": "<="}
- COMPARISON_OPERATORS = frozenset(("==", "!=", "<", ">", "<=", ">="))
- class MisplacedComparisonConstantChecker(BaseChecker):
- """Checks the placement of constants in comparisons"""
- __implements__ = (IAstroidChecker,)
- # 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,
- ):
- 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.check_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):
- """Required method to auto register this checker."""
- linter.register_checker(MisplacedComparisonConstantChecker(linter))
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