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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 unregister_namespace(self, namespace):
 """ Unregister a namespace. :param namespace: Namespace tag. :type namespace: str """

        if namespace not in self._namespaces:
            raise NoRegisteredError("Namespace '{0}' is not registered on loader.".format(namespace))

        del self._namespaces[namespace]