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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 namespace(self, prefix=None):
 """ Get this properties namespace @param prefix: The default prefix. @type prefix: str @return: The schema's target namespace @rtype: (I{prefix},I{URI}) """

        ns = self.schema.tns
        if ns[0] is None:
            ns = (prefix, ns[1])
        return ns