Fix crash on checking private members on __class__

Closes #5261

Author: DanielNoord

ChangeLog

@@ -140,6 +140,10 @@ Release date: TBA
 
   Closes #5216
 
+* Fix crash for ``unused-private-member`` when checking private members on ``__class__``
+
+  Closes #5261
+
 * Added new checker ``useless-with-lock`` to find incorrect usage of with statement and threading module locks.
   Emitted when ``with threading.Lock():`` is used instead of ``with lock_instance:``.
 

doc/whatsnew/2.12.rst

@@ -118,6 +118,10 @@ Other Changes
 
   Closes #3688
 
+* Fix crash for ``unused-private-member`` when checking private members on ``__class__``
+
+  Closes #5261
+
 * Fix double emitting of ``not-callable`` on inferrable ``properties``
 
   Closes #4426

pylint/checkers/classes.py

@@ -945,6 +945,7 @@ def _check_unused_private_functions(self, node: nodes.ClassDef) -> None:
                 )
 
     def _check_unused_private_variables(self, node: nodes.ClassDef) -> None:
+        """Check if private variables are never used within a class"""
         for assign_name in node.nodes_of_class(nodes.AssignName):
             if isinstance(assign_name.parent, nodes.Arguments):
                 continue  # Ignore function arguments
@@ -953,12 +954,15 @@ def _check_unused_private_variables(self, node: nodes.ClassDef) -> None:
             for child in node.nodes_of_class((nodes.Name, nodes.Attribute)):
                 if isinstance(child, nodes.Name) and child.name == assign_name.name:
                     break
-                if (
-                    isinstance(child, nodes.Attribute)
-                    and child.attrname == assign_name.name
-                    and child.expr.name in ("self", "cls", node.name)
-                ):
-                    break
+                if isinstance(child, nodes.Attribute):
+                    if not isinstance(child.expr, nodes.Name):
+                        break
+                    if child.attrname == assign_name.name and child.expr.name in (
+                        "self",
+                        "cls",
+                        node.name,
+                    ):
+                        break
             else:
                 args = (node.name, assign_name.name)
                 self.add_message("unused-private-member", node=assign_name, args=args)

tests/functional/u/unused/unused_private_member.py

@@ -300,3 +300,12 @@ def __get_fur_color(self):  # [unused-private-member]
 
 def lookup_attribute(mapping, key):
     return mapping[key]
+
+
+# Test for regression on checking __class__ attribute
+# See: https://github.com/PyCQA/pylint/issues/5261
+class Foo:
+    __ham = 1
+
+    def method(self):
+        print(self.__class__.__ham)