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# Licensed under the GPL: https://www.gnu.org/licenses/old-licenses/gpl-2.0.html
# For details: https://github.com/pylint-dev/pylint/blob/main/LICENSE
# Copyright (c) https://github.com/pylint-dev/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))
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