python将“字符串”转为二进制形式

def change(str):
    s=""   
    for n in range(len(str)):
        if(n+1)%2!=0:
            s=s+"\\x"+str[n];
            # if len(str) == (n+1):
            #     print(s)
        else:
            s = s + str[n];
            # print(s)

    return s