Fix false-positive of unused-private-member with class name

ChangeLog

@@ -60,6 +60,10 @@ Release date: TBA
 
   Closes #4673
 
+* Fix a false positive for ``unused-private-member`` with class names
+
+  Closes #4681
+
 
 What's New in Pylint 2.9.6?
 ===========================

pylint/checkers/classes.py

@@ -974,6 +974,7 @@ def _check_unused_private_variables(self, node: astroid.ClassDef) -> None:
 
     def _check_unused_private_attributes(self, node: astroid.ClassDef) -> None:
         for assign_attr in node.nodes_of_class(astroid.AssignAttr):
+            assign_attr = cast(astroid.AssignAttr, assign_attr)
             if not is_attr_private(assign_attr.attrname):
                 continue
 
@@ -992,20 +993,29 @@ def _check_unused_private_attributes(self, node: astroid.ClassDef) -> None:
                 )
 
             for attribute in node.nodes_of_class(astroid.Attribute):
-                if attribute.attrname == assign_attr.attrname and (
-                    (
-                        # If assigned to cls.attrib, can be accessed by cls/self
-                        assign_attr.expr.name == "cls"
-                        and attribute.expr.name in ("cls", "self")
-                    )
+                attribute = cast(astroid.Attribute, attribute)
+                if attribute.attrname != assign_attr.attrname:
+                    continue
+
+                if assign_attr.expr.name == "cls" and attribute.expr.name in (
+                    "cls",
+                    "self",
+                ):
+                    # If assigned to cls.attrib, can be accessed by cls/self
+                    break
+
+                if (
+                    assign_attr.expr.name in acceptable_obj_names
+                    and attribute.expr.name == "self"
+                ):
                     # If assigned to self.attrib, can only be accessed by self
                     # Or if __new__ was used, the returned object names are acceptable
-                    or (
-                        assign_attr.expr.name in acceptable_obj_names
-                        and attribute.expr.name == "self"
-                    )
-                ):
                     break
+
+                if assign_attr.expr.name == attribute.expr.name == node.name:
+                    # Recognise attributes which are accessed via the class name
+                    break
+
             else:
                 args = (node.name, assign_attr.attrname)
                 self.add_message("unused-private-member", node=assign_attr, args=args)

tests/functional/u/unused/unused_private_member.py

@@ -201,3 +201,25 @@ def __inner_4():  # [unused-private-member]
 
         fn_to_return = __inner_1 if flag else __inner_3(__inner_2)
         return fn_to_return
+
+
+# https://github.com/PyCQA/pylint/issues/4681
+# Accessing attributes of the class using the class name should not result in a false positive
+# as long as it is used within the class
+class FalsePositive4681:
+    __instance = None
+    __should_cause_error = None  # [unused-private-member]
+    @staticmethod
+    def instance():
+        if FalsePositive4681.__instance is None:
+            FalsePositive4681()
+        return FalsePositive4681.__instance
+
+    def __init__(self):
+        try:
+            FalsePositive4681.__instance = 42  # This should be fine
+            FalsePositive4681.__should_cause_error = True  # [unused-private-member]
+        except Exception:  # pylint: disable=broad-except
+            print("Error")
+            FalsePositive4681.__instance = False  # This should be fine
+            FalsePositive4681.__should_cause_error = False  # [unused-private-member]

tests/functional/u/unused/unused_private_member.txt

@@ -9,3 +9,6 @@ unused-private-member:132:8:FalsePositive4657.__init__:Unused private member `Fa
 undefined-variable:137:15:FalsePositive4657.attr_c:Undefined variable 'cls':HIGH
 unused-private-member:179:8:FalsePositive4673.do_thing.__true_positive:Unused private member `FalsePositive4673.do_thing.__true_positive(in_thing)`:HIGH
 unused-private-member:199:8:FalsePositive4673.complicated_example.__inner_4:Unused private member `FalsePositive4673.complicated_example.__inner_4()`:HIGH
+unused-private-member:211:4:FalsePositive4681:Unused private member `FalsePositive4681.__should_cause_error`:HIGH
+unused-private-member:221:12:FalsePositive4681.__init__:Unused private member `FalsePositive4681.__should_cause_error`:HIGH
+unused-private-member:225:12:FalsePositive4681.__init__:Unused private member `FalsePositive4681.__should_cause_error`:HIGH