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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_map(self, target):
 """Returns the namespace_map used for Thrift generation. :param target: The target to extract the namespace_map from. :type target: :class:`pants.backend.codegen.targets.java_thrift_library.JavaThriftLibrary` :returns: The namespaces to remap (old to new). :rtype: dictionary """

    self._check_target(target)
    return target.namespace_map or self._default_namespace_map