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# Copyright (c) 2016 Alexander Todorov <atodorov@otb.bg>
# Copyright (c) 2017-2018, 2020 Claudiu Popa <pcmanticore@gmail.com>
# Copyright (c) 2019, 2021 Pierre Sassoulas <pierre.sassoulas@gmail.com>
# Copyright (c) 2020 hippo91 <guillaume.peillex@gmail.com>
# Copyright (c) 2020 Anthony Sottile <asottile@umich.edu>
# Copyright (c) 2021 Daniël van Noord <13665637+DanielNoord@users.noreply.github.com>
# Copyright (c) 2021 Marc Mueller <30130371+cdce8p@users.noreply.github.com>
# Copyright (c) 2021 bernie gray <bfgray3@users.noreply.github.com>
# 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
"""Looks for comparisons to zero."""
import itertools
from typing import TYPE_CHECKING, Any, Iterable
import astroid
from astroid import nodes
from pylint import checkers, interfaces
from pylint.checkers import utils
if TYPE_CHECKING:
from pylint.lint import PyLinter
def _is_constant_zero(node):
return isinstance(node, astroid.Const) and node.value == 0
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!
"""
__implements__ = (interfaces.IAstroidChecker,)
# configuration section name
name = "compare-to-zero"
msgs = {
"C2001": (
"Avoid comparisons to zero",
"compare-to-zero",
"Used when Pylint detects comparison to a 0 constant.",
)
}
priority = -2
options = ()
@utils.check_messages("compare-to-zero")
def visit_compare(self, node: nodes.Compare) -> None:
_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 = [("", node.left)]
ops.extend(node.ops)
iter_ops: Iterable[Any] = iter(ops)
ops = list(itertools.chain(*iter_ops))
for ops_idx in range(len(ops) - 2):
op_1 = ops[ops_idx]
op_2 = ops[ops_idx + 1]
op_3 = ops[ops_idx + 2]
error_detected = False
# 0 ?? X
if _is_constant_zero(op_1) and op_2 in _operators:
error_detected = True
# X ?? 0
elif op_2 in _operators and _is_constant_zero(op_3):
error_detected = True
if error_detected:
self.add_message("compare-to-zero", node=node)
def register(linter: "PyLinter") -> None:
linter.register_checker(CompareToZeroChecker(linter))
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