code: def holes(self):
          '''Return holes in collection.
  
          Return :py:class:`~clique.collection.Collection` of missing indexes.
  
          '''
          missing = set([])
          previous = None
          for index in self.indexes:
              if previous is None:
                  previous = index
                  continue
  
              if index != (previous + 1):
                  missing.update(range(previous + 1, index))
  
              previous = index
  
          return Collection(self.head, self.tail, self.padding, indexes=missingf holes(self):
          '''Return holes in collection.
  
          Return :py:class:`~clique.collection.Collection` of missing indexes.
  
          '''
          missing = set([])
          previous = None
          for index in self.indexes:
              if previous is None:
                  previous = index
                  continue
  
              if index != (previous + 1):
                  missing.update(range(previous + 1, index))
  
              previous = index
  
          return Collection(self.head, self.tail, self.padding, indexes=missing)
docs: Return holes in collection.
  
          Return :py:class:`~clique.collection.Collection` of missing indexes.