docs: def connected_transformer(network, busids):
      """ Get transformer connected to given buses.
  
      Parameters
      ----------
      network : :class:`pypsa.Network
          Overall container of PyPSA
      busids  : list
          List containing bus-ids.
  
      Returns
      -------
      :class:`pandas.DataFrame
          PyPSA transformer.
      """
  
      mask = (network.transformers.bus0.isin(busids))
  
      return network.transformers[mask]