تمثيل خطوات الطلب بإستخدام State Machine

allowed = {
    'draft': {'submitted'},
    'submitted': {'approved', 'rejected'},
    'approved': set(),
    'rejected': set(),
}
def transition(current, target):
    if target not in allowed[current]:
        return current
    return target

print(transition('draft', 'approved'))
print(transition('submitted', 'approved'))

draft
approved