code: def _extractCreations(self, dataSets):
          
          for dataSet in dataSets:
              modelObject = self._objectFromID(dataSet[self._IDENTIFIER_KEY])
              if modelObject is self._NO_OBJECT_MARKER:
                  dataCopy = dataSet.copy()
                  identifier = dataCopy.pop(self._IDENTIFIER_KEY)
                  yield identifier, dataCopy
docs: Find the elements of C{dataSets} which represent the creation of new
          objects.
  
          @param dataSets: C{list} of C{dict} mapping C{unicode} form submission
              keys to form submission values.
  
          @return: iterator of C{tuple}s with the first element giving the opaque
              identifier of an object which is to be created and the second
              element giving a C{dict} of all the other creation arguments.