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.

8 files changed, 30 insertions, 31 deletions

diff --git a/sphinx/deprecation.py b/sphinx/deprecation.py
index 7cdb1d3d1..57f4b3ddf 100644
--- a/sphinx/deprecation.py
+++ b/sphinx/deprecation.py
@@ -31,10 +31,7 @@ RemovedInNextVersionWarning = RemovedInSphinx30Warning
 
 def deprecated_alias(modname, objects, warning):
     # type: (str, Dict, Type[Warning]) -> None
-    module = sys.modules.get(modname)
-    if module is None:
-        module = import_module(modname)
-
+    module = import_module(modname)
     sys.modules[modname] = _ModuleWrapper(module, modname, objects, warning)  # type: ignore
 
 
diff --git a/sphinx/ext/autodoc/importer.py b/sphinx/ext/autodoc/importer.py
index fc934958d..54901be44 100644
--- a/sphinx/ext/autodoc/importer.py
+++ b/sphinx/ext/autodoc/importer.py
@@ -8,7 +8,7 @@
     :license: BSD, see LICENSE for details.
 """
 
-import sys
+import importlib
 import traceback
 import warnings
 from collections import namedtuple
@@ -23,14 +23,13 @@ logger = logging.getLogger(__name__)
 
 def import_module(modname: str, warningiserror: bool = False) -> Any:
     """
-    Call __import__(modname), convert exceptions to ImportError
+    Call importlib.import_module(modname), convert exceptions to ImportError
     """
     try:
         with warnings.catch_warnings():
             warnings.filterwarnings("ignore", category=ImportWarning)
             with logging.skip_warningiserror(not warningiserror):
-                __import__(modname)
-                return sys.modules[modname]
+                return importlib.import_module(modname)
     except BaseException as exc:
         # Importing modules may cause any side effects, including
         # SystemExit, so we need to catch all errors.
diff --git a/sphinx/ext/coverage.py b/sphinx/ext/coverage.py
index 24f51b856..7d53e7bb9 100644
--- a/sphinx/ext/coverage.py
+++ b/sphinx/ext/coverage.py
@@ -13,6 +13,7 @@ import glob
 import inspect
 import pickle
 import re
+from importlib import import_module
 from os import path
 from typing import Any, Dict, IO, List, Pattern, Set, Tuple
 
@@ -144,7 +145,7 @@ class CoverageBuilder(Builder):
                 continue
 
             try:
-                mod = __import__(mod_name, fromlist=['foo'])
+                mod = import_module(mod_name)
             except ImportError as err:
                 logger.warning(__('module %s could not be imported: %s'), mod_name, err)
                 self.py_undoc[mod_name] = {'error': err}
diff --git a/sphinx/ext/inheritance_diagram.py b/sphinx/ext/inheritance_diagram.py
index f52a990bf..ecb6302d1 100644
--- a/sphinx/ext/inheritance_diagram.py
+++ b/sphinx/ext/inheritance_diagram.py
@@ -38,8 +38,8 @@ r"""
 import builtins
 import inspect
 import re
-import sys
 from hashlib import md5
+from importlib import import_module
 from typing import Any, Dict, Iterable, List, Tuple
 from typing import cast
 
@@ -74,8 +74,10 @@ def try_import(objname: str) -> Any:
     Returns imported object or module.  If failed, returns None value.
     """
     try:
-        __import__(objname)
-        return sys.modules.get(objname)
+        return import_module(objname)
+    except TypeError:
+        # Relative import
+        return None
     except ImportError:
         matched = module_sig_re.match(objname)
 
@@ -87,8 +89,8 @@ def try_import(objname: str) -> Any:
         if modname is None:
             return None
         try:
-            __import__(modname)
-            return getattr(sys.modules.get(modname), attrname, None)
+            module = import_module(modname)
+            return getattr(module, attrname, None)
         except ImportError:
             return None
 
diff --git a/sphinx/highlighting.py b/sphinx/highlighting.py
index b4e63209f..977b71f28 100644
--- a/sphinx/highlighting.py
+++ b/sphinx/highlighting.py
@@ -11,6 +11,7 @@
 import html
 import warnings
 from functools import partial
+from importlib import import_module
 
 from pygments import highlight
 from pygments.filters import ErrorToken
@@ -92,7 +93,7 @@ class PygmentsBridge:
             return NoneStyle
         elif '.' in stylename:
             module, stylename = stylename.rsplit('.', 1)
-            return getattr(__import__(module, None, None, ['__name__']), stylename)
+            return getattr(import_module(module), stylename)
         else:
             return get_style_by_name(stylename)
 
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(
diff --git a/sphinx/search/__init__.py b/sphinx/search/__init__.py
index 1b4f7ea59..22ba14d40 100644
--- a/sphinx/search/__init__.py
+++ b/sphinx/search/__init__.py
@@ -11,6 +11,7 @@ import html
 import pickle
 import re
 import warnings
+from importlib import import_module
 from os import path
 
 from docutils import nodes
@@ -278,8 +279,7 @@ class IndexBuilder:
             self.lang = SearchEnglish(options)  # type: SearchLanguage
         elif isinstance(lang_class, str):
             module, classname = lang_class.rsplit('.', 1)
-            lang_class = getattr(__import__(module, None, None, [classname]),
-                                 classname)
+            lang_class = getattr(import_module(module), classname)
             self.lang = lang_class(options)
         else:
             # it's directly a class (e.g. added by app.add_search_language)
diff --git a/sphinx/util/__init__.py b/sphinx/util/__init__.py
index f06720695..b75e80034 100644
--- a/sphinx/util/__init__.py
+++ b/sphinx/util/__init__.py
@@ -22,6 +22,7 @@ from codecs import BOM_UTF8
 from collections import deque
 from datetime import datetime
 from hashlib import md5
+from importlib import import_module
 from os import path
 from time import mktime, strptime
 from typing import Any, Callable, Dict, IO, Iterable, Iterator, List, Pattern, Set, Tuple
@@ -270,12 +271,10 @@ def get_module_source(modname: str) -> Tuple[str, str]:
     Can return ('file', 'filename') in which case the source is in the given
     file, or ('string', 'source') which which case the source is the string.
     """
-    if modname not in sys.modules:
-        try:
-            __import__(modname)
-        except Exception as err:
-            raise PycodeError('error importing %r' % modname, err)
-    mod = sys.modules[modname]
+    try:
+        mod = import_module(modname)
+    except Exception as err:
+        raise PycodeError('error importing %r' % modname, err)
     filename = getattr(mod, '__file__', None)
     loader = getattr(mod, '__loader__', None)
     if loader and getattr(loader, 'get_filename', None):
@@ -316,8 +315,7 @@ def get_full_modname(modname: str, attribute: str) -> str:
         # Prevents a TypeError: if the last getattr() call will return None
         # then it's better to return it directly
         return None
-    __import__(modname)
-    module = sys.modules[modname]
+    module = import_module(modname)
 
     # Allow an attribute to have multiple parts and incidentially allow
     # repeated .s in the attribute.
@@ -572,14 +570,13 @@ def import_object(objname: str, source: str = None) -> Any:
     try:
         objpath = objname.split('.')
         modname = objpath.pop(0)
-        obj = __import__(modname)
+        obj = import_module(modname)
         for name in objpath:
             modname += '.' + name
             try:
                 obj = getattr(obj, name)
             except AttributeError:
-                __import__(modname)
-                obj = getattr(obj, name)
+                obj = import_module(modname)
 
         return obj
     except (AttributeError, ImportError) as exc: