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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 getSigned(self, ns_uri, ns_key, default=None):
 """Return the specified signed field if available, otherwise return default """

        if self.isSigned(ns_uri, ns_key):
            return self.message.getArg(ns_uri, ns_key, default)
        else:
            return default