code: def rain_series(self):
          
          return [(tstamp, \
                  self._station_history.get_measurements()[tstamp]['rain']) \
                  for tstamp in self._station_history.get_measurements()]
docs: Returns the precipitation time series relative to the
          meteostation, in the form of a list of tuples, each one containing the
          couple timestamp-value
  
          :returns: a list of tuples