我在 python 中使用 open() 命令时遇到问题

Question

I am currently developing a desktop login-register app for my practice, and was having some trouble with login and register. If I type REGISTER and add my info in f.write() command it stores my info but after that everything just goes, like the whole file gets formatted (this was register issue).

The login issue is if I want to check whether a name or password in file exists or not (this command could be wrong). I tried to use if login_email and login password in f: but it says that login_email and password do not exist.

Code:

f = open('pass.txt', 'w')
fr = open('pass.txt', 'r')
from time import sleep

login_list = "LOGIN"
register_list = "REGISTER"

if 1 > -3232:
    print("Type register for new account\ntype login for login into existing account")
    bi = input("==>    ")

    if bi.upper() in login_list:
        print("you are registered?? nice now loginnn!!")
        login_1 = input("your username:   ")
        login_2 = input("your password:   ")
        if login_1 and login_2 in fr:
            print("Nice my program worked??")
            exit()
        else:
            exit()

    elif bi.upper() in register_list:
        print("you are in register section: ")
        sleep(.9)
        print("NOTE:  Your password should only contain alphabets!")
        sleep(4)
        reg_1 = input("your username:     ")
        sleep(.9)
        reg_2 = input("your password:     ")
        sleep(.9)
        reg_2v1 = input("confirm password")
        if reg_2 == reg_2v1:
            f.write(reg_1 + " : " + reg_2 + "\n")
            print("now login again,\")
        else:
            print("invalid password, try again")

    else:
        print("you gave me the wrong command")

else:
    exit()

Answer 1

1. You shouldn't open the file in both read and write mode at the beginning of the script. Opening it in write mode empties the file, so you won't be able to read it. You'll also wipe out all the other usernames and passwords. You should open the file in read mode when logging in, and append mode when registering, to add a new line without removing the old ones. And you should use with to just open the file around the code that needs to use it.
2. if login_1 and login_2 in fr: is not the correct way to test if both the username and password are in the file. Due to operator precedence, that's parsed as if login_1 and (login_2 in fr): . This just checks that login_1 is not empty, and then just checks if login_2 is in the file. The second test will never work, because the lines of the file all end with newline, but login_2 doesn't, so they'll never match.

You need to check for the fully formatted line, including the newline.

if f'{login_1} : {login_2}\n' in fr:

3. if bi.upper() in login_list: seems suspicious. login_list is not a list, it's a string. So this will check whether bi.upper() is any substring -- it will succeed if the user enters log or in or gi , not just login . Is that intentional?

Full code:

from time import sleep

login_list = "LOGIN"
register_list = "REGISTER"

if 1 > -3232:
    print("Type register for new account\ntype login for login into existing account")
    bi = input("==>    ")

    if bi.upper() in login_list:
        print("you are registered?? nice now loginnn!!")
        login_1 = input("your username:   ")
        login_2 = input("your password:   ")
        with open('pass.txt', 'r') as fr:
            if f'{login_1} : {login_2}\n' in fr:
                print("Nice my program worked??")
                exit()
            else:
                exit()

    elif bi.upper() in register_list:
        print("you are in register section: ")
        sleep(.9)
        print("NOTE:  Your password should only contain alphabets!")
        sleep(4)
        reg_1 = input("your username:     ")
        sleep(.9)
        reg_2 = input("your password:     ")
        sleep(.9)
        reg_2v1 = input("confirm password")
        if reg_2 == reg_2v1:
            with open('pass.txt', 'a') as f:
                f.write(reg_1 + " : " + reg_2 + "\n")
            print("now login again,")
        else:
            print("invalid password, try again")

    else:
        print("you gave me the wrong command")

else:
    exit()