code: def add_and_get(self, delta):
          '''
          Atomically adds `delta` to the current value.
  
          :param delta: The delta to add.
          '''
          with self._reference.get_lock():
              self._reference.value += delta
              return self._reference.valuf add_and_get(self, delta):
          '''
          Atomically adds `delta` to the current value.
  
          :param delta: The delta to add.
          '''
          with self._reference.get_lock():
              self._reference.value += delta
              return self._reference.value
docs: Atomically adds `delta` to the current value.
  
          :param delta: The delta to add.