old_contents: class ApplianceTrace(object):
  
      def __init__(self, series):
          self.series = series
  
      def get_series(self):
          return self.series
  
new_contents: class ApplianceTrace(object):
  
      def __init__(self, series, source):
          '''
          Initializes a trace object from a series and a source.
          Series must be sampled at a particular sample rate
          '''
          self.series = series
          self.source = source
  
      def get_series(self):
          return self.series
  
      def get_source(self):
          return self.series
  
      def get_sampling_rate(self):
          return self.series.index.freq
  
subject: update appliance trace