code: def index(self, id, *args):
          
          # because values are unique, start and stop are not relevant
          if isinstance(id, string_types):
              try:
                  return self._dict[id]
              except KeyError:
                  raise ValueError("%s not found" % id)
          try:
              i = self._dict[id.id]
              if self[i] is not id:
                  raise ValueError(
                      "Another object with the identical id (%s) found" % id.id)
              return i
          except KeyError:
              raise ValueError("%s not found" % str(id))
docs: Determine the position in the list
  
          id: A string or a :class:`~cobra.core.Object.Object`