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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
# 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))
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