code: def declare(self, name):
          
  
          if name in self._data:
              raise KeyError("Declared name {} that already existed".format(name))
  
          self._data[name] = self._loop.create_future()
docs: Declare that a key will be set in the future.
  
          This will create a future for the key that is used to
          hold its result and allow awaiting it.
  
          Args:
              name (str): The unique key that will be used.