name : comparetozero.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 """Looks for comparisons to zero.""" from __future__ import annotations import itertools from typing import TYPE_CHECKING import astroid from astroid import nodes from pylint import checkers from pylint.checkers import utils from pylint.interfaces import HIGH if TYPE_CHECKING: from pylint.lint import PyLinter def _is_constant_zero(node: str | nodes.NodeNG) -> bool: # We have to check that node.value is not False because node.value == 0 is True # when node.value is False return ( isinstance(node, astroid.Const) and node.value == 0 and node.value is not False ) class CompareToZeroChecker(checkers.BaseChecker): """Checks for comparisons to zero. Most of the time you should use the fact that integers with a value of 0 are false. An exception to this rule is when 0 is allowed in the program and has a different meaning than None! """ # configuration section name name = "compare-to-zero" msgs = { "C2001": ( '"%s" can be simplified to "%s" as 0 is falsey', "compare-to-zero", "Used when Pylint detects comparison to a 0 constant.", ) } options = () @utils.only_required_for_messages("compare-to-zero") def visit_compare(self, node: nodes.Compare) -> None: # pylint: disable=duplicate-code _operators = ["!=", "==", "is not", "is"] # note: astroid.Compare has the left most operand in node.left # while the rest are a list of tuples in node.ops # the format of the tuple is ('compare operator sign', node) # here we squash everything into `ops` to make it easier for processing later ops: list[tuple[str, nodes.NodeNG]] = [("", node.left)] ops.extend(node.ops) iter_ops = iter(ops) all_ops = list(itertools.chain(*iter_ops)) for ops_idx in range(len(all_ops) - 2): op_1 = all_ops[ops_idx] op_2 = all_ops[ops_idx + 1] op_3 = all_ops[ops_idx + 2] error_detected = False # 0 ?? X if _is_constant_zero(op_1) and op_2 in _operators: error_detected = True op = op_3 # X ?? 0 elif op_2 in _operators and _is_constant_zero(op_3): error_detected = True op = op_1 if error_detected: original = f"{op_1.as_string()} {op_2} {op_3.as_string()}" suggestion = ( op.as_string() if op_2 in {"!=", "is not"} else f"not {op.as_string()}" ) self.add_message( "compare-to-zero", args=(original, suggestion), node=node, confidence=HIGH, ) def register(linter: PyLinter) -> None: linter.register_checker(CompareToZeroChecker(linter))