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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def to_representation(self, instance):
 """ If we have a serializer mapping, use that. Otherwise, use standard serializer behavior Since we might be dealing with multiple indexes, some fields might not be valid for all results. Do not render the fields which don't belong to the search result. """

        if self.Meta.serializers:
            ret = self.multi_serializer_representation(instance)
        else:
            ret = super(HaystackSerializer, self).to_representation(instance)
            prefix_field_names = len(getattr(self.Meta, "index_classes")) > 1
            current_index = self._get_index_class_name(type(instance.searchindex))
            for field in self.fields.keys():
                # handle declared field value methods on serializer
                value_method = getattr(self, "get_{}".format(field), None)
                if value_method and callable(value_method):
                    ret[field] = value_method()

                # now convert namespaced field names
                orig_field = field
                if prefix_field_names:
                    parts = field.split("__")
                    if len(parts) > 1:
                        index = parts[0][1:]  # trim the preceding '_'
                        field = parts[1]
                        if index == current_index:
                            ret[field] = ret[orig_field]
                        del ret[orig_field]
                elif field not in chain(instance.searchindex.fields.keys(), self._declared_fields.keys()):
                    del ret[orig_field]

        # include the highlighted field in either case
        if getattr(instance, "highlighted", None):
            ret["highlighted"] = instance.highlighted[0]
        return ret