Explain a little more.

Lib/threading.py

@@ -172,6 +172,7 @@ def _acquire_restore(self, x):
         self.__lock.acquire()           # Ignore saved state
 
     def _is_owned(self):
+        # Return True if lock is owned by currentThread.
         # This method is called only if __lock doesn't have _is_owned().
         if self.__lock.acquire(0):
             self.__lock.release()