name : modified_iterating_checker.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 typing import TYPE_CHECKING from astroid import nodes from pylint import checkers, interfaces from pylint.checkers import utils if TYPE_CHECKING: from pylint.lint import PyLinter _LIST_MODIFIER_METHODS = {"append", "remove"} _SET_MODIFIER_METHODS = {"add", "remove"} class ModifiedIterationChecker(checkers.BaseChecker): """Checks for modified iterators in for loops iterations. Currently supports `for` loops for Sets, Dictionaries and Lists. """ name = "modified_iteration" msgs = { "W4701": ( "Iterated list '%s' is being modified inside for loop body, consider iterating through a copy of it " "instead.", "modified-iterating-list", "Emitted when items are added or removed to a list being iterated through. " "Doing so can result in unexpected behaviour, that is why it is preferred to use a copy of the list.", ), "E4702": ( "Iterated dict '%s' is being modified inside for loop body, iterate through a copy of it instead.", "modified-iterating-dict", "Emitted when items are added or removed to a dict being iterated through. " "Doing so raises a RuntimeError.", ), "E4703": ( "Iterated set '%s' is being modified inside for loop body, iterate through a copy of it instead.", "modified-iterating-set", "Emitted when items are added or removed to a set being iterated through. " "Doing so raises a RuntimeError.", ), } options = () @utils.only_required_for_messages( "modified-iterating-list", "modified-iterating-dict", "modified-iterating-set" ) def visit_for(self, node: nodes.For) -> None: iter_obj = node.iter for body_node in node.body: self._modified_iterating_check_on_node_and_children(body_node, iter_obj) def _modified_iterating_check_on_node_and_children( self, body_node: nodes.NodeNG, iter_obj: nodes.NodeNG ) -> None: """See if node or any of its children raises modified iterating messages.""" self._modified_iterating_check(body_node, iter_obj) for child in body_node.get_children(): self._modified_iterating_check_on_node_and_children(child, iter_obj) def _modified_iterating_check( self, node: nodes.NodeNG, iter_obj: nodes.NodeNG ) -> None: msg_id = None if isinstance(node, nodes.Delete) and any( self._deleted_iteration_target_cond(t, iter_obj) for t in node.targets ): inferred = utils.safe_infer(iter_obj) if isinstance(inferred, nodes.List): msg_id = "modified-iterating-list" elif isinstance(inferred, nodes.Dict): msg_id = "modified-iterating-dict" elif isinstance(inferred, nodes.Set): msg_id = "modified-iterating-set" elif not isinstance(iter_obj, (nodes.Name, nodes.Attribute)): pass elif self._modified_iterating_list_cond(node, iter_obj): msg_id = "modified-iterating-list" elif self._modified_iterating_dict_cond(node, iter_obj): msg_id = "modified-iterating-dict" elif self._modified_iterating_set_cond(node, iter_obj): msg_id = "modified-iterating-set" if msg_id: if isinstance(iter_obj, nodes.Attribute): obj_name = iter_obj.attrname else: obj_name = iter_obj.name self.add_message( msg_id, node=node, args=(obj_name,), confidence=interfaces.INFERENCE, ) @staticmethod def _is_node_expr_that_calls_attribute_name(node: nodes.NodeNG) -> bool: return ( isinstance(node, nodes.Expr) and isinstance(node.value, nodes.Call) and isinstance(node.value.func, nodes.Attribute) and isinstance(node.value.func.expr, nodes.Name) ) @staticmethod def _common_cond_list_set( node: nodes.Expr, iter_obj: nodes.Name | nodes.Attribute, infer_val: nodes.List | nodes.Set, ) -> bool: iter_obj_name = ( iter_obj.attrname if isinstance(iter_obj, nodes.Attribute) else iter_obj.name ) return (infer_val == utils.safe_infer(iter_obj)) and ( # type: ignore[no-any-return] node.value.func.expr.name == iter_obj_name ) @staticmethod def _is_node_assigns_subscript_name(node: nodes.NodeNG) -> bool: return isinstance(node, nodes.Assign) and ( isinstance(node.targets[0], nodes.Subscript) and (isinstance(node.targets[0].value, nodes.Name)) ) def _modified_iterating_list_cond( self, node: nodes.NodeNG, iter_obj: nodes.Name | nodes.Attribute ) -> bool: if not self._is_node_expr_that_calls_attribute_name(node): return False infer_val = utils.safe_infer(node.value.func.expr) if not isinstance(infer_val, nodes.List): return False return ( self._common_cond_list_set(node, iter_obj, infer_val) and node.value.func.attrname in _LIST_MODIFIER_METHODS ) def _modified_iterating_dict_cond( self, node: nodes.NodeNG, iter_obj: nodes.Name | nodes.Attribute ) -> bool: if not self._is_node_assigns_subscript_name(node): return False # Do not emit when merely updating the same key being iterated if ( isinstance(iter_obj, nodes.Name) and iter_obj.name == node.targets[0].value.name and isinstance(iter_obj.parent.target, nodes.AssignName) and isinstance(node.targets[0].slice, nodes.Name) and iter_obj.parent.target.name == node.targets[0].slice.name ): return False infer_val = utils.safe_infer(node.targets[0].value) if not isinstance(infer_val, nodes.Dict): return False if infer_val != utils.safe_infer(iter_obj): return False if isinstance(iter_obj, nodes.Attribute): iter_obj_name = iter_obj.attrname else: iter_obj_name = iter_obj.name return node.targets[0].value.name == iter_obj_name # type: ignore[no-any-return] def _modified_iterating_set_cond( self, node: nodes.NodeNG, iter_obj: nodes.Name | nodes.Attribute ) -> bool: if not self._is_node_expr_that_calls_attribute_name(node): return False infer_val = utils.safe_infer(node.value.func.expr) if not isinstance(infer_val, nodes.Set): return False return ( self._common_cond_list_set(node, iter_obj, infer_val) and node.value.func.attrname in _SET_MODIFIER_METHODS ) def _deleted_iteration_target_cond( self, node: nodes.DelName, iter_obj: nodes.NodeNG ) -> bool: if not isinstance(node, nodes.DelName): return False if not isinstance(iter_obj.parent, nodes.For): return False if not isinstance( iter_obj.parent.target, (nodes.AssignName, nodes.BaseContainer) ): return False return any( t == node.name for t in utils.find_assigned_names_recursive(iter_obj.parent.target) ) def register(linter: PyLinter) -> None: linter.register_checker(ModifiedIterationChecker(linter))