old_contents: from abc import *
  
  
  class Topology(ABCMeta):
      @abstractmethod
      def __init__(self):
          self.bonds = None
          self.angles = None
          self.
  
new_contents: from abc import *
  
  
  class Topology(ABCMeta):
      @abstractmethod
      def __init__(self):
          self.bonds = None
          self.angles = None
          self.dihedrals = None
  
subject: Fix topology