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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 get_allowed(allow, disallow):
 """ Normalize the given string attributes as a list of all allowed vClasses."""

    if allow is None and disallow is None:
        return SUMO_VEHICLE_CLASSES
    elif disallow is None:
        return allow.split()
    else:
        disallow = disallow.split()
        return tuple([c for c in SUMO_VEHICLE_CLASSES if c not in disallow])