old_contents: """
  This file contains the base class to calculate weights for each
  state
  """
  
  class StateWeight(object):
      """
      Provides facilities for calculating the weight of a given state
      (such as a molecule, or mutant).
      
      Arguments
      ---------
      proposal : namedtuple of type TopologyProposal
          Contains the newly-proposed topology and
          associated metadata.
  
      Properties
      ----------
      weight : float, read only
          The calculated weight of this state
      """
      
      def __init__(self, proposal):
          pass
  
      @property
      def weight(self):
          pass
  
new_contents: """
  This file contains the base class to calculate weights for each
  state
  """
  
  class StateWeight(object):
      """
      Provides facilities for calculating the weight of a given state
      (such as a molecule, or mutant).
      
      Arguments
      ---------
      proposal : namedtuple of type TopologyProposal
          Contains the newly-proposed topology and
          associated metadata.
  
      Properties
      ----------
      weight : float, read only
          The calculated log weight of this state
      """
      
      def __init__(self, proposal):
          pass
  
      @property
      def weight(self):
          return 0
  
subject: return dummy weight from weight_calculation