# 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
from __future__ import annotations
from itertools import zip_longest
from typing import TYPE_CHECKING
from astroid import nodes
from pylint.checkers import BaseChecker
from pylint.interfaces import HIGH
if TYPE_CHECKING:
from pylint.lint import PyLinter
class LambdaExpressionChecker(BaseChecker):
"""Check for unnecessary usage of lambda expressions."""
name = "lambda-expressions"
msgs = {
"C3001": (
"Lambda expression assigned to a variable. "
'Define a function using the "def" keyword instead.',
"unnecessary-lambda-assignment",
"Used when a lambda expression is assigned to variable "
'rather than defining a standard function with the "def" keyword.',
),
"C3002": (
"Lambda expression called directly. Execute the expression inline instead.",
"unnecessary-direct-lambda-call",
"Used when a lambda expression is directly called "
"rather than executing its contents inline.",
),
}
options = ()
def visit_assign(self, node: nodes.Assign) -> None:
"""Check if lambda expression is assigned to a variable."""
if isinstance(node.targets[0], nodes.AssignName) and isinstance(
node.value, nodes.Lambda
):
self.add_message(
"unnecessary-lambda-assignment",
node=node.value,
confidence=HIGH,
)
elif isinstance(node.targets[0], nodes.Tuple) and isinstance(
node.value, (nodes.Tuple, nodes.List)
):
# Iterate over tuple unpacking assignment elements and
# see if any lambdas are assigned to a variable.
# N.B. We may encounter W0632 (unbalanced-tuple-unpacking)
# and still need to flag the lambdas that are being assigned.
for lhs_elem, rhs_elem in zip_longest(
node.targets[0].elts, node.value.elts
):
if lhs_elem is None or rhs_elem is None:
# unbalanced tuple unpacking. stop checking.
break
if isinstance(lhs_elem, nodes.AssignName) and isinstance(
rhs_elem, nodes.Lambda
):
self.add_message(
"unnecessary-lambda-assignment",
node=rhs_elem,
confidence=HIGH,
)
def visit_namedexpr(self, node: nodes.NamedExpr) -> None:
if isinstance(node.target, nodes.AssignName) and isinstance(
node.value, nodes.Lambda
):
self.add_message(
"unnecessary-lambda-assignment",
node=node.value,
confidence=HIGH,
)
def visit_call(self, node: nodes.Call) -> None:
"""Check if lambda expression is called directly."""
if isinstance(node.func, nodes.Lambda):
self.add_message(
"unnecessary-direct-lambda-call",
node=node,
confidence=HIGH,
)
def register(linter: PyLinter) -> None:
linter.register_checker(LambdaExpressionChecker(linter))
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