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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
"""Checks for magic values instead of literals."""
from __future__ import annotations
from re import match as regex_match
from typing import TYPE_CHECKING
from astroid import nodes
from pylint.checkers import BaseChecker, utils
from pylint.interfaces import HIGH
if TYPE_CHECKING:
from pylint.lint import PyLinter
class MagicValueChecker(BaseChecker):
"""Checks for constants in comparisons."""
name = "magic-value"
msgs = {
"R2004": (
"Consider using a named constant or an enum instead of '%s'.",
"magic-value-comparison",
"Using named constants instead of magic values helps improve readability and maintainability of your"
" code, try to avoid them in comparisons.",
)
}
options = (
(
"valid-magic-values",
{
"default": (0, -1, 1, "", "__main__"),
"type": "csv",
"metavar": "<argument names>",
"help": "List of valid magic values that `magic-value-compare` will not detect. "
"Supports integers, floats, negative numbers, for empty string enter ``''``,"
" for backslash values just use one backslash e.g \\n.",
},
),
)
def __init__(self, linter: PyLinter) -> None:
"""Initialize checker instance."""
super().__init__(linter=linter)
self.valid_magic_vals: tuple[float | str, ...] = ()
def open(self) -> None:
# Extra manipulation is needed in case of using external configuration like an rcfile
if self._magic_vals_ext_configured():
self.valid_magic_vals = tuple(
self._parse_rcfile_magic_numbers(value)
for value in self.linter.config.valid_magic_values
)
else:
self.valid_magic_vals = self.linter.config.valid_magic_values
def _magic_vals_ext_configured(self) -> bool:
return not isinstance(self.linter.config.valid_magic_values, tuple)
def _check_constants_comparison(self, node: nodes.Compare) -> None:
"""
Magic values in any side of the comparison should be avoided,
Detects comparisons that `comparison-of-constants` core checker cannot detect.
"""
const_operands = []
LEFT_OPERAND = 0
RIGHT_OPERAND = 1
left_operand = node.left
const_operands.append(isinstance(left_operand, nodes.Const))
right_operand = node.ops[0][1]
const_operands.append(isinstance(right_operand, nodes.Const))
if all(const_operands):
# `comparison-of-constants` avoided
return
operand_value = None
if const_operands[LEFT_OPERAND] and self._is_magic_value(left_operand):
operand_value = left_operand.value
elif const_operands[RIGHT_OPERAND] and self._is_magic_value(right_operand):
operand_value = right_operand.value
if operand_value is not None:
self.add_message(
"magic-value-comparison",
node=node,
args=(operand_value),
confidence=HIGH,
)
def _is_magic_value(self, node: nodes.Const) -> bool:
return (not utils.is_singleton_const(node)) and (
node.value not in (self.valid_magic_vals)
)
@staticmethod
def _parse_rcfile_magic_numbers(parsed_val: str) -> float | str:
parsed_val = parsed_val.encode().decode("unicode_escape")
if parsed_val.startswith("'") and parsed_val.endswith("'"):
return parsed_val[1:-1]
is_number = regex_match(r"[-+]?\d+(\.0*)?$", parsed_val)
return float(parsed_val) if is_number else parsed_val
@utils.only_required_for_messages("magic-comparison")
def visit_compare(self, node: nodes.Compare) -> None:
self._check_constants_comparison(node)
def register(linter: PyLinter) -> None:
linter.register_checker(MagicValueChecker(linter))
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