docs: def subscribe(self, event, hook):
          """
          Subscribe a callback to an event
  
          Parameters
          ----------
          event : str
              Available events are 'precall', 'postcall', and 'capacity'.
              precall is called with: (connection, command, query_kwargs)
              postcall is called with: (connection, command, query_kwargs, response)
              capacity is called with: (connection, command, query_kwargs, response, capacity)
          hook : callable
  
          """
          if hook not in self._hooks[event]:
              self._hooks[event].append(hook)