reverse_bin.py

def reverse_bits(n):
    assert 1 <= n <= 1000000000,\
        'argument must be in range [1, 1000000000]'
    r = 0
    while n:
        r <<= 1
        r |= n & 1
        n >>= 1
    return r


if __name__ == '__main__':
    import sys
    if len(sys.argv) > 1 and sys.argv[1].isdigit():
        print(reverse_bits(int(sys.argv[1])))
    else:
        print('Usage: {} <N>'.format(sys.argv[0]))