如何将多行文本文件分解为可以迭代的列表，以检查 python 中的输入 == 文本文件？

Question

When running the Code I get a logic error where it continues to throw the first if statement error "Error! Username does not exist." I need to be able to log in as admin and then add users by adding them to a .txt file, after which, if the program is run again, I can log in either by admin or one of the new users created in the txt file. I cant seem to get it split properly in order for the loop to iterate through the list correctly when login in.

Example:

print(new_lines) = [['admin', 'adm1n'], ['kevin', 'kev1n'], ['dorothy', '1234']]

.txt file content with each entry on new line = admin,adm1n\\n kevin,kev1n\\n dorothy,1234

Code thus far:

import time

#User input of username and password

user_name = input("Username:\n")
user_pass = input("Password: \n")

#Opening document

with open("user.txt", "r+", encoding = "utf-8-sig") as f:
    
    new_lines = []
    for line in f:
        new_line = line.strip()
        new_lines.append(new_line.split(","))
        
    print(new_lines)

    #Loop to enter user name and password
    for x in new_lines:
        for y in x:
            if user_name != new_lines[:][0]:
                print("Error! Username does not exist.")
                user_name = input("Username:\n")
                user_pass = input("Password: \n")
                
            elif user_pass != new_lines[:][1]:
                print("Error! Incorrect password.")
                user_name = input("Username:\n")
                user_pass = input("Password: \n")
                
            else:
                print("Welcome back!")
                break
        break
        
    #User options to choose from        
    user_choice = input("""\nPlease select one of the following options:
                            \nr - register user
                            \na - add task 
                            \nva - view all tasks
                            \nvm - view my tasks
                            \ne - exit
                            \nAnswer: """)

Answer 1

I recommend reformatting the code a little to make it easier to find if the username exists and if the password is correct.

import time

#User input of username and password

user_name = input("Username:\n")
user_pass = input("Password: \n")

#Opening document

with open("user.txt", "r+", encoding = "utf-8-sig") as f:
    
    new_lines = []
    for line in f:
        new_line = line.strip()
        new_lines.append(new_line.split(","))

usernames = [acc[0] for acc in new_lines]
pws = [acc[1] for acc in new_lines]

while True:
    if user_name not in usernames:
        print("Error! Username does not exist.")
        user_name = input("Username:\n")
        user_pass = input("Password: \n")
    else:
        pw_index = usernames.index(user_name)
        if user_pass != pws[pw_index]:
            print("Error! Incorrect password.")
            user_name = input("Username:\n")
            user_pass = input("Password: \n")
        else:
            print("Welcome back!")
            break

#User options to choose from        
user_choice = input("""\nPlease select one of the following options:
                        \nr - register user
                        \na - add task 
                        \nva - view all tasks
                        \nvm - view my tasks
                        \ne - exit
                        \nAnswer: """)

Answer 2

You have a logic error in the loop - you seem to compare every line in the text file to the username and password provided, and state an error if they dont match - ignoring the fact that the user may not be on the first line of the file. The error should only be displayed if you went through the entire file and didnt find the user, or found the user but the password mismatches.

Also, I dont think you want the inner loop at all, you declare x and y but dont use them, have you tried printing them and checking what they hold?

Anyway, this is the outline of how I think the loop should look

found = False
for current_user, current_password in new_lines:
    if current_user == user_name:
        if current_password == user_pass:
            print("Welcome back!")
            found = True
        else:
            print("Error! Incorrect password")
       break
if not found:
    print("Error! Username does not exist.")