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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 smart_search(cls, query_string, search_options=None, extra_query = None):
 """ Perform a smart prefix search. Maps to the function :py:func:`nipap.backend.Nipap.smart_search_prefix` in the backend. Please see the documentation for the backend function for information regarding input arguments and return values. """


        if search_options is None:
            search_options = {}

        xmlrpc = XMLRPCConnection()
        try:
            smart_result = xmlrpc.connection.smart_search_prefix(
                {
                    'query_string': query_string,
                    'search_options': search_options,
                    'auth': AuthOptions().options,
                    'extra_query': extra_query
                })
        except xmlrpclib.Fault as xml_fault:
            raise _fault_to_exception(xml_fault)
        result = dict()
        result['interpretation'] = smart_result['interpretation']
        result['search_options'] = smart_result['search_options']
        result['error'] = smart_result['error']
        if 'error_message' in smart_result:
            result['error_message'] = smart_result['error_message']
        result['result'] = list()
        for prefix in smart_result['result']:
            p = Prefix.from_dict(prefix)
            result['result'].append(p)

        return result