Do not invoke descriptors or metaclass __getattr__()

Add Python pseudo-code in the doc.

Author: vstinner

Doc/c-api/type.rst

@@ -311,13 +311,30 @@ Type Objects
 
    Look for a type attribute through the type
    :term:`MRO <method resolution order>`.
+   Do not invoke descriptors or metaclass ``__getattr__``.
 
    *name* must be a :class:`str`.
 
    * If found, set *\*attr* to a :term:`strong reference` and return ``1``.
    * If not found, set *\*attr* to ``NULL`` and return ``0``.
    * On error, set an exception and return ``-1``.
 
+   Python pseudo-code (return :exc:`AttributeError` if not found instead of
+   raising an exception)::
+
+       def PyType_Lookup(type, name):
+           if not isinstance(name, str):
+               raise TypeError
+
+           for klass in type.mro():
+               try:
+                   return klass.__dict__[name]
+               except KeyError:
+                   pass
+
+           # not found
+           return AttributeError
+
    .. versionadded:: next
 
    .. seealso::

Lib/test/test_capi/test_type.py

@@ -278,14 +278,31 @@ def test_extension_managed_dict_type(self):
     def test_type_lookup(self):
         type_lookup = _testcapi.type_lookup
 
-        class Parent:
+        class Meta(type):
+            def __getattr__(self, name):
+                if name == "meta_attr":
+                    return "meta attr"
+                else:
+                    raise AttributeError
+
+        class Ten:
+            def __get__(self, obj, objtype=None):
+                return 10
+
+        class Parent(metaclass=Meta):
             parent_attr = "parent"
+            attr = "parent"
 
         class Child(Parent):
-            child_attr = "child"
+            attr = "child"
+            descr = Ten()
 
         self.assertEqual(type_lookup(Child, "parent_attr"), "parent")
-        self.assertEqual(type_lookup(Child, "child_attr"), "child")
+        self.assertEqual(type_lookup(Child, "attr"), "child")
+        self.assertEqual(type_lookup(Child, "descr"), Child.__dict__['descr'])
+        self.assertEqual(Child.descr, 10)
+        self.assertEqual(type_lookup(Child, "meta_attr"), AttributeError)
+        self.assertEqual(Child.meta_attr, "meta attr")
         self.assertEqual(type_lookup(Child, "xxx"), AttributeError)
 
         # name parameter must be a str