与python补码相关的一个程序

请写Python程序，输入x、y是十进制的正数或负数，介于-128-127之间，输出z=x+y。首先转为8位二进制数，进行加法运算x+y，然后留下8位转为十进制数。例如x=-2，y=3，首先x变成11111110，y变成00000011，x+y=100000001，保留8位，输出+1。需要注意的是，如有溢出，则需返回错误，否则返回十进制结果。判断方法采用：正数+正数，若8位二进制数最高位为1，则溢出；负数+负数，若8位二进制数最高位为0，则溢出。溢出需在二进制结果上直接判断！

def bincontent(x, y):
    x = "{:08b}".format(x & 0b11111111)
    y = "{:08b}".format(y & 0b11111111)
    new = ''
    mark = False
    for i in range(7, -1,-1):
        if x[i] == "0" and y[i] == "0":
            if mark:
                new = "1" + new
                mark = False
            else:
                new = "0" + new
        elif x[i] == "1" and y[i] == "1":
            if mark:
                new = "1" + new
                mark = True
            else:
                new = "0" + new

                mark = True
        else:
            if mark:
                new = "0" + new
                mark = True
            else:
                new = "1" + new
    else:
        if mark:
            new = "1" + new
    if new[0]=="1" and int(new,2)>128:
        return "error"
    else:
        return int(new,2)


print(bincontent(65, 65))
print(bincontent(-64, -64))
print(bincontent(64, 64))

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