old_contents: from astropy.time import Time
  
  
  def which_epi_janus_resonance(name, time):
      """Find which swap situtation we are in by time.
  
      Starting from 2006-01-21 where a Janus-Epimetheus swap occured, and
      defining the next 4 years until the next swap as `scenario1, and the 4
      years after that `scenario2`.
      Calculate in units of 4 years, in which scenario the given time falls.
  
      Parameters
      ----------
      time : timestring, datetime
          Time of the image. The astropy Time object can deal with both formats.
  
      Returns
      -------
      str
          The given name string (either `janus` or `epimetheus`) and attach
          a 1 or 2, as appropriate.
      """
      t1 = Time('2002-01-21').to_datetime()
      delta = Time(time).to_datetime() - t1
      yearfraction = delta.days / 365
      if int(yearfraction / 4) % 2 == 0:
          return name + '2'
      else:
          return name + '1'
  
new_contents: from astropy.time import Time
  
  
  def which_epi_janus_resonance(name, time):
      """Find which swap situtation we are in by time.
  
      Starting from 2006-01-21 where a Janus-Epimetheus swap occured, and
      defining the next 4 years until the next swap as `scenario1, and the 4
      years after that `scenario2`.
      Calculate in units of 4 years, in which scenario the given time falls.
  
      Parameters
      ----------
      time : timestring, datetime
          Time of the image. The astropy Time object can deal with both formats.
  
      Returns
      -------
      str
          The given name string (either `janus` or `epimetheus`) and attach
          a 1 or 2, as appropriate.
      """
      t1 = Time('2002-01-21').to_datetime()
      delta = Time(time).to_datetime() - t1
      yearfraction = delta.days / 365
      if int(yearfraction / 4) % 2 == 0:
          return name + '2'
      else:
          return name + '1'
  
  
  def filename_from_obsid(obsid):
      tokens = obsid.split('_')
      return f"{tokens[-1]}{tokens[-2]}"
  
subject: add filename_from_obsid