输入密码，成功后显示欢迎，输入三次锁定，保存错误

user_name = 'Hello world'
password = '321321'
url = 'D:\7z' #似乎没用到
answer1 = input('请输入用户名\n')
answer2 = input('请输入密码\n')
if answer1 == user_name and answer2 == password:
    print('ok,welcome')
else :
    answer1 = input('agqin')
    answer2 = input('again')
    count = 2
    while count >0 :
        answer1 = input('agqin')
        answer2 = input('again')
        if answer2 !=password:
            count = count -1
            with open('D:\\7z\\a\\1.txt','w') as f:
                f.write('count = 0',)
                f.close()
        else:
            print('good,welcome')

变量全部大写字母表示常量，例如π = 3.1415.....

1位=1bit

8bit = 1byte = 1字节

cd../../..返回多层目录