Reimplement fix for #4019

sphinx/ext/inheritance_diagram.py

@@ -76,11 +76,13 @@ def try_import(objname):
         __import__(objname)
         return sys.modules.get(objname)  # type: ignore
     except ImportError:
-        try:
-            modname, attrname = module_sig_re.match(objname).groups()  # type: ignore
-        except AttributeError:
+        matched = module_sig_re.match(objname)  # type: ignore
+
+        if not matched:
             return None
-        else:
+
+        modname, attrname = matched.groups()
+
         if modname is None:
             return None
         try: