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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 create_response_signature(self, string_message, zone):
 """ Basic helper function to keep code clean for defining a response message signature """


        zz = ''
        if zone is not None:
            zz = hex(int(zone)-1).replace('0x', '')  # RNET requires zone value to be zero based
        string_message = string_message.replace('@zz', zz)  # Replace zone parameter
        return string_message