Fix too-many-ancestors

ChangeLog

@@ -2,13 +2,24 @@
 Pylint's ChangeLog
 ------------------
 
-What's New in Pylint 2.8.2?
+What's New in Pylint 2.8.3?
 ===========================
 Release date: 2021-04-26
 
 ..
   Put new features and bugfixes here and also in 'doc/whatsnew/2.9.rst'
 
+* Fix false-positive ``too-many-ancestors`` when inheriting from builtin classes,
+  especially from the ``collections.abc`` module
+
+  Closes #4166
+  Closes #4415
+
+
+What's New in Pylint 2.8.2?
+===========================
+Release date: 2021-04-26
+
 * Keep ``__pkginfo__.numversion`` a tuple to avoid breaking pylint-django.
 
   Closes #4405
@@ -22,9 +33,6 @@ What's New in Pylint 2.8.1?
 ===========================
 Release date: 2021-04-25
 
-..
-  Put new features and bugfixes here and also in 'doc/whatsnew/2.9.rst'
-
 * Add numversion back (temporarily) in ``__pkginfo__`` because it broke Pylama and revert the unnecessary
   ``pylint.version`` breaking change.
 

doc/whatsnew/2.9.rst

@@ -16,3 +16,6 @@ Other Changes
 =============
 
 * Pylint's tags are now the standard form ``vX.Y.Z`` and not ``pylint-X.Y.Z`` anymore.
+
+* Fix false-positive ``too-many-ancestors`` when inheriting from builtin classes,
+  especially from the ``collections.abc`` module

pylint/checkers/design_analysis.py

@@ -26,6 +26,7 @@
 from collections import defaultdict
 
 import astroid
+from astroid import nodes
 
 from pylint import utils
 from pylint.checkers import BaseChecker
@@ -97,6 +98,87 @@
 TYPING_NAMEDTUPLE = "typing.NamedTuple"
 TYPING_TYPEDDICT = "typing.TypedDict"
 
+# Set of stdlib classes to ignore when calculating number of ancestors
+STDLIB_CLASSES_IGNORE_ANCESTOR = frozenset(
+    (
+        "builtins.object",
+        "builtins.tuple",
+        "builtins.dict",
+        "builtins.list",
+        "builtins.set",
+        "bulitins.frozenset",
+        "collections.ChainMap",
+        "collections.Counter",
+        "collections.OrderedDict",
+        "collections.UserDict",
+        "collections.UserList",
+        "collections.UserString",
+        "collections.defaultdict",
+        "collections.deque",
+        "collections.namedtuple",
+        "_collections_abc.Awaitable",
+        "_collections_abc.Coroutine",
+        "_collections_abc.AsyncIterable",
+        "_collections_abc.AsyncIterator",
+        "_collections_abc.AsyncGenerator",
+        "_collections_abc.Hashable",
+        "_collections_abc.Iterable",
+        "_collections_abc.Iterator",
+        "_collections_abc.Generator",
+        "_collections_abc.Reversible",
+        "_collections_abc.Sized",
+        "_collections_abc.Container",
+        "_collections_abc.Collection",
+        "_collections_abc.Set",
+        "_collections_abc.MutableSet",
+        "_collections_abc.Mapping",
+        "_collections_abc.MutableMapping",
+        "_collections_abc.MappingView",
+        "_collections_abc.KeysView",
+        "_collections_abc.ItemsView",
+        "_collections_abc.ValuesView",
+        "_collections_abc.Sequence",
+        "_collections_abc.MutableSequence",
+        "_collections_abc.ByteString",
+        "typing.Tuple",
+        "typing.List",
+        "typing.Dict",
+        "typing.Set",
+        "typing.FrozenSet",
+        "typing.Deque",
+        "typing.DefaultDict",
+        "typing.OrderedDict",
+        "typing.Counter",
+        "typing.ChainMap",
+        "typing.Awaitable",
+        "typing.Coroutine",
+        "typing.AsyncIterable",
+        "typing.AsyncIterator",
+        "typing.AsyncGenerator",
+        "typing.Iterable",
+        "typing.Iterator",
+        "typing.Generator",
+        "typing.Reversible",
+        "typing.Container",
+        "typing.Collection",
+        "typing.AbstractSet",
+        "typing.MutableSet",
+        "typing.Mapping",
+        "typing.MutableMapping",
+        "typing.Sequence",
+        "typing.MutableSequence",
+        "typing.ByteString",
+        "typing.MappingView",
+        "typing.KeysView",
+        "typing.ItemsView",
+        "typing.ValuesView",
+        "typing.ContextManager",
+        "typing.AsyncContextManger",
+        "typing.Hashable",
+        "typing.Sized",
+    )
+)
+
 
 def _is_exempt_from_public_methods(node: astroid.ClassDef) -> bool:
     """Check if a class is exempt from too-few-public-methods"""
@@ -294,9 +376,13 @@ def _ignored_argument_names(self):
         "too-few-public-methods",
         "too-many-public-methods",
     )
-    def visit_classdef(self, node):
+    def visit_classdef(self, node: nodes.ClassDef):
         """check size of inheritance hierarchy and number of instance attributes"""
-        nb_parents = len(list(node.ancestors()))
+        nb_parents = sum(
+            1
+            for ancestor in node.ancestors()
+            if ancestor.qname() not in STDLIB_CLASSES_IGNORE_ANCESTOR
+        )
         if nb_parents > self.config.max_parents:
             self.add_message(
                 "too-many-ancestors",

tests/functional/t/too/too_many_ancestors.py

@@ -1,4 +1,5 @@
 # pylint: disable=missing-docstring, too-few-public-methods, useless-object-inheritance
+from collections.abc import MutableSequence
 
 class Aaaa(object):
     pass
@@ -22,3 +23,23 @@ class Iiii(Aaaa, Bbbb, Cccc, Dddd, Eeee, Ffff, Gggg, Hhhh): # [too-many-ancestor
 
 class Jjjj(Iiii): # [too-many-ancestors]
     pass
+
+
+# https://github.com/PyCQA/pylint/issues/4166
+# https://github.com/PyCQA/pylint/issues/4415
+class ItemSequence(MutableSequence):
+    """Minimal MutableSequence."""
+    def __getitem__(self, key):
+        return key
+
+    def __setitem__(self, key, value):
+        _ = key, value
+
+    def __delitem__(self, key):
+        _ = key
+
+    def insert(self, index, value):
+        _ = index, value
+
+    def __len__(self):
+        return 1

tests/functional/t/too/too_many_ancestors.txt

@@ -1,2 +1,2 @@
-too-many-ancestors:20:0:Iiii:Too many ancestors (9/7)
-too-many-ancestors:23:0:Jjjj:Too many ancestors (10/7)
+too-many-ancestors:21:0:Iiii:Too many ancestors (8/7)
+too-many-ancestors:24:0:Jjjj:Too many ancestors (9/7)