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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 combine_locks(locks):
 """Combine a sequence of locks into a single lock."""

    all_locks = []
    for lock in locks:
        if isinstance(lock, CombinedLock):
            all_locks.extend(lock.locks)
        elif lock is not None:
            all_locks.append(lock)

    num_locks = len(all_locks)
    if num_locks > 1:
        return CombinedLock(all_locks)
    elif num_locks == 1:
        return all_locks[0]
    else:
        return DummyLock()