old_contents: from __future__ import division, absolute_import, print_function
  
  from .selectspecred import SelectSpecRedGalaxies
  from .redsequencecal import RedSequenceCalibrator
  
new_contents: from __future__ import division, absolute_import, print_function
  
  from .selectspecred import SelectSpecRedGalaxies
  from .redsequencecal import RedSequenceCalibrator
  from .centeringcal import WcenCalibrator
  
  
subject: Add WcenCalibrator