old_contents: from ApplianceTrace import ApplianceTrace
  from ApplianceInstance import ApplianceInstance
  from ApplianceType import ApplianceType
  from ApplianceSet import ApplianceSet
  
new_contents: from ApplianceTrace import ApplianceTrace
  from ApplianceInstance import ApplianceInstance
  from ApplianceType import ApplianceType
  from ApplianceSet import ApplianceSet
  
  def concatenate_traces(traces):
      '''
      Given a list of consecutive appliance traces, returns a single concatenated
      trace. Must be sampled at the same rate.
      '''
      pass
  
subject: add concatenate_traces to utils