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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 key_for_namespace(cls, namespace):
 """Return the Key for a namespace. Args: namespace: A string giving the namespace whose key is requested. Returns: The Key for the namespace. """

    if namespace:
      return model.Key(cls.KIND_NAME, namespace)
    else:
      return model.Key(cls.KIND_NAME, cls.EMPTY_NAMESPACE_ID)