Exclude ``__dict__`` from ``attribute-defined-outside-init``

Close #2909

3 files changed, 14 insertions, 1 deletions

diff --git a/ChangeLog b/ChangeLog
index 6ce1d8bfc..a3408dea6 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -7,7 +7,12 @@ What's New in Pylint 2.4.0?
 
 Release date: TBA
 
-* Fix pointer on spelling check when the error are more than one time in the same line. 
+
+* Exclude ``__dict__`` from ``attribute-defined-outside-init``
+
+  Close #2909
+
+* Fix pointer on spelling check when the error are more than one time in the same line.
 
   Close #2895
 
diff --git a/pylint/checkers/classes.py b/pylint/checkers/classes.py
index d75107136..604b8ef45 100644
--- a/pylint/checkers/classes.py
+++ b/pylint/checkers/classes.py
@@ -823,6 +823,9 @@ a metaclass class method.",
             # check if any method attr is defined in is a defining method
             if any(node.frame().name in defining_methods for node in nodes):
                 continue
+            # Exclude `__dict__` as it is already defined.
+            if attr == "__dict__":
+                continue
 
             # check attribute is defined in a parent's __init__
             for parent in cnode.instance_attr_ancestors(attr):
diff --git a/pylint/test/functional/attribute_defined_outside_init.py b/pylint/test/functional/attribute_defined_outside_init.py
index 826b5d68b..ab5cf5f19 100644
--- a/pylint/test/functional/attribute_defined_outside_init.py
+++ b/pylint/test/functional/attribute_defined_outside_init.py
@@ -60,3 +60,8 @@ class Mixin(object):
         """Don't emit attribute-defined-outside-init for mixin classes."""
         if self.defined_already: # pylint: disable=access-member-before-definition
             self.defined_already = None
+
+
+class F:
+    def func(self):
+        self.__dict__ = {'foo': 'bar'}