minor style and performance modification

Author: changhoetyng

mypy/semanal.py

@@ -6407,46 +6407,46 @@ def lookup_fully_qualified_or_none(self, fullname: str) -> SymbolTableNode | Non
         # TODO: unify/clean-up/simplify lookup methods, see #4157.
         # TODO: support nested classes (but consider performance impact,
         #       we might keep the module level only lookup for thing like 'builtins.int').
-        assert "." in fullname
-
-        splitted_modules = fullname.rsplit(".")
-        names = []
-
-        while splitted_modules and ".".join(splitted_modules) not in self.modules:
-            """
-            Try to find the module in the modules dictionary.
+        module, name = fullname.rsplit(".", maxsplit=1)
+
+        if module in self.modules:
+            # If the module exists, look up the name in the module.
+            # This is the common case.
+            filenode = self.modules[module]
+            result = filenode.names.get(name)
+            if result is None and self.is_incomplete_namespace(module):
+                # TODO: More explicit handling of incomplete refs?
+                self.record_incomplete_ref()
+            return result
+        else:
+            # Else, try to find the longest prefix of the module name that is in the modules dictionary.
+            splitted_modules = fullname.split(".")
+            names = []
 
-            If the module is not found, pop the last element of the splitted list and append it to the names list.
+            while splitted_modules and ".".join(splitted_modules) not in self.modules:
+                names.append(splitted_modules.pop())
 
-            This is to find the longest prefix of the module name that is in the modules dictionary.
-            """
-            names.append(splitted_modules.pop())
+            if not splitted_modules or not names:
+                # If no module or name is found, return None.
+                return None
 
-        if not splitted_modules or not names:
-            """
-            If no module or name is found, return None.
-            """
-            return None
+            # Reverse the names list to get the correct order of names.
+            names.reverse()
 
-        """
-        Reverse the names list to get the correct order of names.
-        """
-        names.reverse()
+            module = ".".join(splitted_modules)
+            filenode = self.modules[module]
+            result = filenode.names.get(names[0])
 
-        module = ".".join(splitted_modules)
-        filenode = self.modules[module]
-        result = filenode.names.get(names[0])
-
-        if result is None and self.is_incomplete_namespace(module):
-            # TODO: More explicit handling of incomplete refs?
-            self.record_incomplete_ref()
+            if result is None and self.is_incomplete_namespace(module):
+                # TODO: More explicit handling of incomplete refs?
+                self.record_incomplete_ref()
 
-        for part in names[1:]:
-            if result is not None and isinstance(result.node, TypeInfo):
-                result = result.node.names.get(part)
-            else:
-                return None
-        return result
+            for part in names[1:]:
+                if result is not None and isinstance(result.node, TypeInfo):
+                    result = result.node.names.get(part)
+                else:
+                    return None
+            return result
 
     def object_type(self) -> Instance:
         return self.named_type("builtins.object")