def _map(self, function, iterable, *args, **kwargs):
        return self._type(function(element, *args, **kwargs)
                          for element in iterable)
Handle start of document event
dataset/ETHPy150Open django-nonrel/djangotoolbox/djangotoolbox/fields.py/AbstractIterableField._map--crossover with--dataset/ETHPy150Open AppScale/appscale/AppServer/google/appengine/api/yaml_listener.py/EventHandler.DocumentStart