Classes and Functions

[Low_Ki_]

I was thinking that you want the user to enter the username again after hitting the "Enter" button if thoughts.

While True:
    if prompt_username in names:
        print('The user exists!')
        prompt_username = input(prompt_message)
    else:
        break

Hey, that code actually works perfect! Thank you so much for that. I figured out another way I could do this as well. As far as creating a file if it does not exist already... Thanks for the while loops I don't know why I didn't think to flag it True.
I could probably modify and implement this into my code and use a dict() to read in, check, and append user info to. Username:Password
Example of opening and saving user data:

import json

def greet_user():
    filename = 'username.json'

    try:
        with open(filename) as f_obj:
            username = json.load(f_obj)
    except FileNotFoundError:
        with open(filename, 'w') as f_obj:
            username = input("What is your name? ")
            json.dump(username, f_obj)
            print("We'll remember you when you come back, " + username + "!")
    else:
        print("Welcome back, " + username + "!")

greet_user()

---

Another good example would be to add user info like such:

import json

def get_stored_username():
    filename = 'username.json'
    try:
        with open(filename) as f_obj:
            username = json.load(f_obj)
    except FileNotFoundError:
        return None
    else:
        return username



def greet_user():
    username = get_stored_username()
    if username:
        print("Welcome back, " + username + "!")
    else:
        username = input("What is your name? ")
        filename = 'username.json'
        with open(filename, 'w') as f_obj:
            json.dump(f_obj)
            print("We'll remember you when you come back, " + username + "!")

greet_user()