bpo-42133: update parts of the stdlib to fall back to `__spec__.loader` when `__loader__` is missing (#22929)

Doc/whatsnew/3.10.rst

@@ -186,6 +186,12 @@ by :func:`curses.color_content`, :func:`curses.init_color`,
 support is provided by the underlying ncurses library.
 (Contributed by Jeffrey Kintscher and Hans Petter Jansson in :issue:`36982`.)
 
+doctest
+-------
+
+When a module does not define ``__loader__``, fall back to ``__spec__.loader``.
+(Contributed by Brett Cannon in :issue:`42133`.)
+
 encodings
 ---------
 :func:`encodings.normalize_encoding` now ignores non-ASCII characters.
@@ -198,6 +204,18 @@ Added the *root_dir* and *dir_fd* parameters in :func:`~glob.glob` and
 :func:`~glob.iglob` which allow to specify the root directory for searching.
 (Contributed by Serhiy Storchaka in :issue:`38144`.)
 
+inspect
+-------
+
+When a module does not define ``__loader__``, fall back to ``__spec__.loader``.
+(Contributed by Brett Cannon in :issue:`42133`.)
+
+linecache
+---------
+
+When a module does not define ``__loader__``, fall back to ``__spec__.loader``.
+(Contributed by Brett Cannon in :issue:`42133`.)
+
 os
 --
 
@@ -217,6 +235,12 @@ The :mod:`shelve` module now uses :data:`pickle.DEFAULT_PROTOCOL` by default
 instead of :mod:`pickle` protocol ``3`` when creating shelves.
 (Contributed by Zackery Spytz in :issue:`34204`.)
 
+site
+----
+
+When a module does not define ``__loader__``, fall back to ``__spec__.loader``.
+(Contributed by Brett Cannon in :issue:`42133`.)
+
 sys
 ---
 

Lib/doctest.py

@@ -222,9 +222,13 @@ def _load_testfile(filename, package, module_relative, encoding):
     if module_relative:
         package = _normalize_module(package, 3)
         filename = _module_relative_path(package, filename)
-        if getattr(package, '__loader__', None) is not None:
-            if hasattr(package.__loader__, 'get_data'):
-                file_contents = package.__loader__.get_data(filename)
+        if (loader := getattr(package, '__loader__', None)) is None:
+            try:
+                loader = package.__spec__.loader
+            except AttributeError:
+                pass
+        if hasattr(loader, 'get_data'):
+            file_contents = loader.get_data(filename)
             file_contents = file_contents.decode(encoding)
             # get_data() opens files as 'rb', so one must do the equivalent
             # conversion as universal newlines would do.

Lib/inspect.py

@@ -707,10 +707,13 @@ def getsourcefile(object):
     if os.path.exists(filename):
         return filename
     # only return a non-existent filename if the module has a PEP 302 loader
-    if getattr(getmodule(object, filename), '__loader__', None) is not None:
+    module = getmodule(object, filename)
+    if getattr(module, '__loader__', None) is not None:
+        return filename
+    elif getattr(getattr(module, "__spec__", None), "loader", None) is not None:
         return filename
     # or it is in the linecache
-    if filename in linecache.cache:
+    elif filename in linecache.cache:
         return filename
 
 def getabsfile(object, _filename=None):

Lib/linecache.py

@@ -165,9 +165,14 @@ def lazycache(filename, module_globals):
     if not filename or (filename.startswith('<') and filename.endswith('>')):
         return False
     # Try for a __loader__, if available
-    if module_globals and '__loader__' in module_globals:
-        name = module_globals.get('__name__')
-        loader = module_globals['__loader__']
+    if module_globals and '__name__' in module_globals:
+        name = module_globals['__name__']
+        if (loader := module_globals.get('__loader__')) is None:
+            if spec := module_globals.get('__spec__'):
+                try:
+                    loader = spec.loader
+                except AttributeError:
+                    pass
         get_source = getattr(loader, 'get_source', None)
 
         if name and get_source:

Lib/site.py

@@ -105,8 +105,15 @@ def makepath(*paths):
 def abs_paths():
     """Set all module __file__ and __cached__ attributes to an absolute path"""
     for m in set(sys.modules.values()):
-        if (getattr(getattr(m, '__loader__', None), '__module__', None) not in
-                ('_frozen_importlib', '_frozen_importlib_external')):
+        loader_module = None
+        try:
+            loader_module = m.__loader__.__module__
+        except AttributeError:
+            try:
+                loader_module = m.__spec__.loader.__module__
+            except AttributeError:
+                pass
+        if loader_module not in {'_frozen_importlib', '_frozen_importlib_external'}:
             continue   # don't mess with a PEP 302-supplied __file__
         try:
             m.__file__ = os.path.abspath(m.__file__)

Misc/NEWS.d/next/Library/2020-10-23-15-47-47.bpo-42133.BzizYV.rst

@@ -0,0 +1,2 @@
+Update various modules in the stdlib to fall back on `__spec__.loader` when
+`__loader__` isn't defined on a module.