'Return the fields to export as an iterable of tuples
(name, serialized_value)'

def _get_serialized_fields(self, item, default_value=None, include_empty=None):

    if (include_empty is None):
        include_empty = self.export_empty_fields
    if (self.fields_to_export is None):
        if (include_empty and (not isinstance(item, dict))):
            field_iter = six.iterkeys(item.fields)
        else:
            field_iter = six.iterkeys(item)
    elif include_empty:
        field_iter = self.fields_to_export
    else:
        field_iter = (x for x in self.fields_to_export if (x in item))
    for field_name in field_iter:
        if (field_name in item):
            field = ({} if isinstance(item, dict) else item.fields[field_name])
            value = self.serialize_field(field, field_name, item[field_name])
        else:
            value = default_value
        (yield (field_name, value))
