def pickle_persistent_load(identifier):
    if identifier == 'UNKNOWN': return UNKNOWN
    else: raise pickle.UnpicklingError, 'Invalid persistent id'
Helper for pickling, which allows us to save and restore UNKNOWN,
dataset/ETHPy150Open QuantSoftware/QuantSoftwareToolkit/Legacy/epydoc-3.0.1/epydoc/cli.py/pickle_persistent_load