Argthtjtr

I am new to Python and am having trouble with looping while checking strings in a file. For this program, I am checking to see if a username that the user wants to create already exists. If the username already exists in the file, the program prompts the user to enter another username. The loop ends when the user enters a username that is not in the file. Here is the relevant code:

# Prompting for username and password

username = input("Enter your username: ")

password = input("Enter your password: ")



# open password file

f = open("password.txt", "r")



# while username exists in file

while username in f.read():

    username = input("Enter your username: ")



f.close()

If I enter a username that exists in the password file, the program does prompt me to enter another username; however, when I enter the same username, the program does not stay in the loop. Any ideas on why this is occurring?

When you run f.read() Python will read the file in and then continue onto the next line of the file in the next iteration. It wont go back to the top of the file. So it exits the loop since the username in the next line of the file is either an empty string or another name. To fix this you could use a context manager like so:

# Prompting for username and password

username = input("Enter your username: ")

password = input("Enter your password: ")



# read in the file data

with open('password.txt') as f:

    data = f.read()



# while username exists in file

while username in data:

    username = input("Enter your username: ")

Then depending on how the data is structured in your .txt file then you can call split() on data if it's using a new line.

There is no condition to check whether the new username is in the file or not.

Maybe an easier way to do this would be to use the following approach?

username = input("Enter your username: ")

password = input("Enter your password: ")



# open password file

f = open("password.txt", "r")

data = f.read()



# while username exists in file

while username in data:

    new = input("Enter your username: ")

    if new in data:

        continue

    else:

        break



username = new

f.close()

This is because you are using f.read() in the while condition.
f.read reads the whole content of the file at once and there's nothing else to read from file, leading to the end of while loop.

If you want to check for usernames in the file, I'd suggest you create a list of usernames that you read from the file and use it in your while loop for checking.

If your file has contents:
username1, username2, ...

You can do

listOfUsernames = f.read().split(',')

and then use this for checking in while loop.