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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_entity_group(cls, key):
 """Return the key for the entity group containing key. Args: key: a key for an entity group whose __entity_group__ key you want. Returns: The __entity_group__ key for the entity group containing key. """

    return model.Key(cls.KIND_NAME, cls.ID, parent=key.root())