[3.12] Docs: Test presence of optional extensions with importlib (pythonGH-130445) (python#130466)

* [3.12] Docs: Test presence of optional extensions with importlib (pythonGH-130445)
(cherry picked from commit 3cc9e86)

Co-authored-by: Adam Turner <[email protected]>

Author: AA-Turner

Doc/conf.py

@@ -6,9 +6,10 @@
 # The contents of this file are pickled, so don't put values in the namespace
 # that aren't pickleable (module imports are okay, they're removed automatically).
 
-import importlib
 import os
 import sys
+from importlib import import_module
+from importlib.util import find_spec
 
 # Make our custom extensions available to Sphinx
 sys.path.append(os.path.abspath('tools/extensions'))
@@ -36,14 +37,15 @@
     'sphinx.ext.extlinks',
 ]
 
-# Skip if downstream redistributors haven't installed it
-try:
-    import sphinxext.opengraph  # noqa: F401
-except ImportError:
-    pass
-else:
-    extensions.append('sphinxext.opengraph')
-
+# Skip if downstream redistributors haven't installed them
+_OPTIONAL_EXTENSIONS = ('sphinxext.opengraph',)
+for optional_ext in _OPTIONAL_EXTENSIONS:
+    try:
+        if find_spec(optional_ext) is not None:
+            extensions.append(optional_ext)
+    except (ImportError, ValueError):
+        pass
+del _OPTIONAL_EXTENSIONS
 
 doctest_global_setup = '''
 try:
@@ -66,7 +68,7 @@
 # We look for the Include/patchlevel.h file in the current Python source tree
 # and replace the values accordingly.
 # See Doc/tools/extensions/patchlevel.py
-version, release = importlib.import_module('patchlevel').get_version_info()
+version, release = import_module('patchlevel').get_version_info()
 
 rst_epilog = f"""
 .. |python_version_literal| replace:: ``Python {version}``