bpo-40257: Revert changes to inspect.getdoc() (GH-20073)

Doc/library/inspect.rst

@@ -473,15 +473,12 @@ Retrieving source code
 
    Get the documentation string for an object, cleaned up with :func:`cleandoc`.
    If the documentation string for an object is not provided and the object is
-   a method, a property or a descriptor, retrieve the documentation
+   a class, a method, a property or a descriptor, retrieve the documentation
    string from the inheritance hierarchy.
 
    .. versionchanged:: 3.5
       Documentation strings are now inherited if not overridden.
 
-   .. versionchanged:: 3.9
-      Documentation strings for classes are no longer inherited.
-
 
 .. function:: getcomments(object)
 

Doc/whatsnew/3.9.rst

@@ -846,11 +846,6 @@ Changes in the Python API
   :class:`ftplib.FTP_TLS` as a keyword-only parameter, and the default encoding
   is changed from Latin-1 to UTF-8 to follow :rfc:`2640`.
 
-* :func:`inspect.getdoc` no longer returns docstring inherited from the type
-  of the object or from parent class if it is a class if it is not defined
-  in the object itself.
-  (Contributed by Serhiy Storchaka in :issue:`40257`.)
-
 * :meth:`asyncio.loop.shutdown_default_executor` has been added to
   :class:`~asyncio.AbstractEventLoop`, meaning alternative event loops that
   inherit from it should have this method defined.

Lib/inspect.py

@@ -543,6 +543,17 @@ def _findclass(func):
     return cls
 
 def _finddoc(obj):
+    if isclass(obj):
+        for base in obj.__mro__:
+            if base is not object:
+                try:
+                    doc = base.__doc__
+                except AttributeError:
+                    continue
+                if doc is not None:
+                    return doc
+        return None
+
     if ismethod(obj):
         name = obj.__func__.__name__
         self = obj.__self__
@@ -586,35 +597,23 @@ def _finddoc(obj):
         return None
     for base in cls.__mro__:
         try:
-            doc = _getowndoc(getattr(base, name))
+            doc = getattr(base, name).__doc__
         except AttributeError:
             continue
         if doc is not None:
             return doc
     return None
 
-def _getowndoc(obj):
-    """Get the documentation string for an object if it is not
-    inherited from its class."""
-    try:
-        doc = object.__getattribute__(obj, '__doc__')
-        if doc is None:
-            return None
-        if obj is not type:
-            typedoc = type(obj).__doc__
-            if isinstance(typedoc, str) and typedoc == doc:
-                return None
-        return doc
-    except AttributeError:
-        return None
-
 def getdoc(object):
     """Get the documentation string for an object.
 
     All tabs are expanded to spaces.  To clean up docstrings that are
     indented to line up with blocks of code, any whitespace than can be
     uniformly removed from the second line onwards is removed."""
-    doc = _getowndoc(object)
+    try:
+        doc = object.__doc__
+    except AttributeError:
+        return None
     if doc is None:
         try:
             doc = _finddoc(object)

Lib/pydoc.py

@@ -90,9 +90,101 @@ def pathdirs():
             normdirs.append(normdir)
     return dirs
 
+def _findclass(func):
+    cls = sys.modules.get(func.__module__)
+    if cls is None:
+        return None
+    for name in func.__qualname__.split('.')[:-1]:
+        cls = getattr(cls, name)
+    if not inspect.isclass(cls):
+        return None
+    return cls
+
+def _finddoc(obj):
+    if inspect.ismethod(obj):
+        name = obj.__func__.__name__
+        self = obj.__self__
+        if (inspect.isclass(self) and
+            getattr(getattr(self, name, None), '__func__') is obj.__func__):
+            # classmethod
+            cls = self
+        else:
+            cls = self.__class__
+    elif inspect.isfunction(obj):
+        name = obj.__name__
+        cls = _findclass(obj)
+        if cls is None or getattr(cls, name) is not obj:
+            return None
+    elif inspect.isbuiltin(obj):
+        name = obj.__name__
+        self = obj.__self__
+        if (inspect.isclass(self) and
+            self.__qualname__ + '.' + name == obj.__qualname__):
+            # classmethod
+            cls = self
+        else:
+            cls = self.__class__
+    # Should be tested before isdatadescriptor().
+    elif isinstance(obj, property):
+        func = obj.fget
+        name = func.__name__
+        cls = _findclass(func)
+        if cls is None or getattr(cls, name) is not obj:
+            return None
+    elif inspect.ismethoddescriptor(obj) or inspect.isdatadescriptor(obj):
+        name = obj.__name__
+        cls = obj.__objclass__
+        if getattr(cls, name) is not obj:
+            return None
+        if inspect.ismemberdescriptor(obj):
+            slots = getattr(cls, '__slots__', None)
+            if isinstance(slots, dict) and name in slots:
+                return slots[name]
+    else:
+        return None
+    for base in cls.__mro__:
+        try:
+            doc = _getowndoc(getattr(base, name))
+        except AttributeError:
+            continue
+        if doc is not None:
+            return doc
+    return None
+
+def _getowndoc(obj):
+    """Get the documentation string for an object if it is not
+    inherited from its class."""
+    try:
+        doc = object.__getattribute__(obj, '__doc__')
+        if doc is None:
+            return None
+        if obj is not type:
+            typedoc = type(obj).__doc__
+            if isinstance(typedoc, str) and typedoc == doc:
+                return None
+        return doc
+    except AttributeError:
+        return None
+
+def _getdoc(object):
+    """Get the documentation string for an object.
+
+    All tabs are expanded to spaces.  To clean up docstrings that are
+    indented to line up with blocks of code, any whitespace than can be
+    uniformly removed from the second line onwards is removed."""
+    doc = _getowndoc(object)
+    if doc is None:
+        try:
+            doc = _finddoc(object)
+        except (AttributeError, TypeError):
+            return None
+    if not isinstance(doc, str):
+        return None
+    return inspect.cleandoc(doc)
+
 def getdoc(object):
     """Get the doc string or comments for an object."""
-    result = inspect.getdoc(object) or inspect.getcomments(object)
+    result = _getdoc(object) or inspect.getcomments(object)
     return result and re.sub('^ *\n', '', result.rstrip()) or ''
 
 def splitdoc(doc):
@@ -1669,7 +1761,7 @@ def render_doc(thing, title='Python Library Documentation: %s', forceload=0,
               inspect.isclass(object) or
               inspect.isroutine(object) or
               inspect.isdatadescriptor(object) or
-              inspect.getdoc(object)):
+              _getdoc(object)):
         # If the passed object is a piece of data or an instance,
         # document its available methods instead of its value.
         if hasattr(object, '__origin__'):

Lib/test/test_inspect.py

@@ -439,7 +439,8 @@ class TestRetrievingSourceCode(GetSourceBase):
     @unittest.skipIf(sys.flags.optimize >= 2,
                      "Docstrings are omitted with -O2 and above")
     def test_getdoc_inherited(self):
-        self.assertIsNone(inspect.getdoc(mod.FesteringGob))
+        self.assertEqual(inspect.getdoc(mod.FesteringGob),
+                         'A longer,\n\nindented\n\ndocstring.')
         self.assertEqual(inspect.getdoc(mod.FesteringGob.abuse),
                          'Another\n\ndocstring\n\ncontaining\n\ntabs')
         self.assertEqual(inspect.getdoc(mod.FesteringGob().abuse),
@@ -447,20 +448,10 @@ class TestRetrievingSourceCode(GetSourceBase):
         self.assertEqual(inspect.getdoc(mod.FesteringGob.contradiction),
                          'The automatic gainsaying.')
 
-    @unittest.skipIf(MISSING_C_DOCSTRINGS, "test requires docstrings")
-    def test_getowndoc(self):
-        getowndoc = inspect._getowndoc
-        self.assertEqual(getowndoc(type), type.__doc__)
-        self.assertEqual(getowndoc(int), int.__doc__)
-        self.assertEqual(getowndoc(int.to_bytes), int.to_bytes.__doc__)
-        self.assertEqual(getowndoc(int().to_bytes), int.to_bytes.__doc__)
-        self.assertEqual(getowndoc(int.from_bytes), int.from_bytes.__doc__)
-        self.assertEqual(getowndoc(int.real), int.real.__doc__)
-
     @unittest.skipIf(MISSING_C_DOCSTRINGS, "test requires docstrings")
     def test_finddoc(self):
         finddoc = inspect._finddoc
-        self.assertIsNone(finddoc(int))
+        self.assertEqual(finddoc(int), int.__doc__)
         self.assertEqual(finddoc(int.to_bytes), int.to_bytes.__doc__)
         self.assertEqual(finddoc(int().to_bytes), int.to_bytes.__doc__)
         self.assertEqual(finddoc(int.from_bytes), int.from_bytes.__doc__)

Misc/NEWS.d/next/Library/2020-05-13-23-10-25.bpo-40257.aR4TGp.rst

@@ -0,0 +1 @@
+Revert changes to :func:`inspect.getdoc`.