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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 get_sieve_capabilities(self):
 """Returns the SIEVE extensions supported by the server. They're read from server capabilities. (see the CAPABILITY command) :rtype: string """

        if isinstance(self.__capabilities["SIEVE"], six.string_types):
            self.__capabilities["SIEVE"] = self.__capabilities["SIEVE"].split()
        return self.__capabilities["SIEVE"]