old_contents: 
  from rmgpy.molecule.graph import Graph
  
  class Fragment(Graph):
  
  	def __init__(self,
  				label='',
  				species_repr=None,
  				vertices=None):
  		self.index = -1
  		self.label = label
  		self.species_repr = species_repr
  		Graph.__init__(self, vertices)
  
  	def __str__(self):
  		"""
  		Return a string representation, in the form 'label(id)'.
  		"""
  		if self.index == -1: return self.label
  		else: return '{0}({1:d})'.format(self.label, self.index)
  	
  	## need to rewrite later
  	def _repr_png_(self):
  		if len(self.species_repr.molecule) > 0:
  			return self.species_repr.molecule[0]._repr_png_()
  		else:
  			return None
new_contents: 
  from rmgpy.molecule.graph import Graph, Vertex
  
  class CuttingLabel(Vertex):
  
      def __init__(self, label=''):
          Vertex.__init__(self)
          self.label = label
  
      def __str__(self):
          """
          Return a human-readable string representation of the object.
          """
          return str(self.label)
  
      def __repr__(self):
          """
          Return a representation that can be used to reconstruct the object.
          """
          return "<CuttingLabel '{0}'>".format(str(self))
  
      def isSpecificCaseOf(self, other):
          """
          Return ``True`` if `self` is a specific case of `other`, or ``False``
          otherwise. At this moment, this is the same as the :meth:`equivalent()`.
          """
          return self.equivalent(other)
  
      def equivalent(self, other):
          """
          Return ``True`` if `other` is indistinguishable from this CuttingLabel, or
          ``False`` otherwise. If `other` is an :class:`CuttingLabel` object, then all
          attributes must match exactly. 
          """
          if isinstance(other, CuttingLabel):
              return self.label == other.label
          else:
              return False
  
  class Fragment(Graph):
  
  	def __init__(self,
  				label='',
  				species_repr=None,
  				vertices=None):
  		self.index = -1
  		self.label = label
  		self.species_repr = species_repr
  		Graph.__init__(self, vertices)
  
  	def __str__(self):
  		"""
  		Return a string representation, in the form 'label(id)'.
  		"""
  		if self.index == -1: return self.label
  		else: return '{0}({1:d})'.format(self.label, self.index)
  	
  	## need to rewrite later
  	def _repr_png_(self):
  		if len(self.species_repr.molecule) > 0:
  			return self.species_repr.molecule[0]._repr_png_()
  		else:
  			return None
subject: add CuttingLabel class