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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 req2frame(req, N: int=0):
 """ output has to be numpy.arange for > comparison """

    if req is None:
        frame = np.arange(N, dtype=np.int64)
    elif isinstance(req, int):  # the user is specifying a step size
        frame = np.arange(0, N, req, dtype=np.int64)
    elif len(req) == 1:
        frame = np.arange(0, N, req[0], dtype=np.int64)
    elif len(req) == 2:
        frame = np.arange(req[0], req[1], dtype=np.int64)
    elif len(req) == 3:
        # this is -1 because user is specifying one-based index
        frame = np.arange(req[0], req[1], req[2],
                          dtype=np.int64) - 1  # keep -1 !
    else:  # just return all frames
        frame = np.arange(N, dtype=np.int64)

    return frame