name : lambda_expressions.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 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))