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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 functions(self):
 """ Access the functions :returns: twilio.rest.serverless.v1.service.function.FunctionList :rtype: twilio.rest.serverless.v1.service.function.FunctionList """

        if self._functions is None:
            self._functions = FunctionList(self._version, service_sid=self._solution['sid'], )
        return self._functions