python对txt文件每一行去重

if __name__ == '__main__':
    str1 = []
    with open('stop.txt', 'r') as f:
        for line in f.readlines():
            if line not in str1:
                str1.append(line)

    for str in str1:
        with open('stop_remove_same.txt', "a+") as f:
            f.write(str)

很简单的一个问题，记录以下