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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 contribute_to_class(self, cls, name):
 """ Swap out any reference to ``KeywordsField`` with the ``KEYWORDS_FIELD_string`` field in ``search_fields``. """

        super(KeywordsField, self).contribute_to_class(cls, name)
        string_field_name = list(self.fields.keys())[0] % \
                            self.related_field_name
        if hasattr(cls, "search_fields") and name in cls.search_fields:
            try:
                weight = cls.search_fields[name]
            except TypeError:
                # search_fields is a sequence.
                index = cls.search_fields.index(name)
                search_fields_type = type(cls.search_fields)
                cls.search_fields = list(cls.search_fields)
                cls.search_fields[index] = string_field_name
                cls.search_fields = search_fields_type(cls.search_fields)
            else:
                del cls.search_fields[name]
                cls.search_fields[string_field_name] = weight