以下Python代码实现 位的格雷码，则横线上应填写（ ）。
def generate_gray_code(n):
if n <= 0:
return []
if n == 1:
return [0, 1]
gray_code = generate_gray_code(n - 1)
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for x in gray_code]
return gray_code + inverted_gray_code
inverted_gray_code = [int(('0' * n + bin(x)[2:])[-n:], 2)
inverted_gray_code = [int(('1' * n + bin(x)[2:])[-n:], 2)
inverted_gray_code = [int(('1' * n + bin(x)[1:])[-n:], 2)
inverted_gray_code = [int(('1' * n + bin(x)[2:])[n:], 2)