Switch uses of __import__ to importlib.get_module()

The Python docs for __import__ recommend using importlib.get_module().

https://docs.python.org/3/library/functions.html#__import__

> Note: This is an advanced function that is not needed in everyday
> Python programming, unlike importlib.import_module().

As importlib.get_module() uses the Python module cache and returns the
module, this also allows simplifying many module cache checks of use of
sys.modules.

importlib.get_module() has been available since Python 3.3.

1 files changed, 5 insertions, 3 deletions

diff --git a/sphinx/registry.py b/sphinx/registry.py
index f8ee39466..3666c758b 100644
--- a/sphinx/registry.py
+++ b/sphinx/registry.py
@@ -10,6 +10,7 @@
 
 import traceback
 import warnings
+from importlib import import_module
 from inspect import isclass
 from types import MethodType
 
@@ -471,18 +472,19 @@ class SphinxComponentRegistry:
         prefix = __('while setting up extension %s:') % extname
         with prefixed_warnings(prefix):
             try:
-                mod = __import__(extname, None, None, ['setup'])
+                mod = import_module(extname)
             except ImportError as err:
                 logger.verbose(__('Original exception:\n') + traceback.format_exc())
                 raise ExtensionError(__('Could not import extension %s') % extname, err)
 
-            if not hasattr(mod, 'setup'):
+            setup = getattr(mod, 'setup', None)
+            if setup is None:
                 logger.warning(__('extension %r has no setup() function; is it really '
                                   'a Sphinx extension module?'), extname)
                 metadata = {}  # type: Dict[str, Any]
             else:
                 try:
-                    metadata = mod.setup(app)
+                    metadata = setup(app)
                 except VersionRequirementError as err:
                     # add the extension name to the version required
                     raise VersionRequirementError(