def convert(input_bytes):
    output = bytearray(len(input_bytes))
    for i in range(0, len(input_bytes), 4):
        output[i + 3] = input_bytes[i + 0]
        output[i + 0] = input_bytes[i + 1]
        output[i + 1] = input_bytes[i + 2]
        output[i + 2] = input_bytes[i + 3]
    return output

test_input = b'argb' * 10
test_output = convert(test_input)
assert test_output == b'rgba' * 10