docs: def _remove_pairs(self, ids_to_remove):
          """Remove the pairs identified by the given indices into _pairs.
          
          Removes the pair, and updates the _key_ids mapping to be accurate.
          Removing the ids from the _key_ids is your own responsibility.
          
          Params:
              ids_to_remove -- The indices to remove. MUST be sorted.
          
          """
          # Remove them.
          for i in reversed(ids_to_remove):
              del self._pairs[i]
          
          # We use the bisect to tell us how many spots the given index is
          # shifting up in the list.
          for ids in self._key_ids.itervalues():
              for i, id in enumerate(ids):
                  ids[i] -= bisect(ids_to_remove, id)