Authentication

db = MySQLdb.connect("localhost", "root", "7May1996", "login_sys")


# Check if username is valid
# @param username {String} - Username to be checked for existance
# @returns {Boolean} - If there are multiple table records
# with matching username then user exists and function returns TRUE, otherwise FALSE.
def usernameExists(username)
    cursor = db.cursor()
    cursor.execute('SELECT COUNT(*) FROM users WHERE user_name = %s', (username,))
    username_match_count = cursor.fetchone()
    db.close()
    return username_match_count[0] > 0


# Inserts user into a table
# @param username {String} - Username
# @param password {String} - Password
def insertUser(username, password)
    cursor = db.cursor()
    cursor.execute('INSERT INTO users (user_name, user_password) VALUES ("%s", "%s")', (username, password))
    db.commit()
    db.close()


# Getting an input value. Input can be anything and this needs to be validated
# to suit a particular criteria. Unput must be 1 or 2.
# Username and password can also be retrieved because they are both required down the line
# for both options.
user_choice = input("Test login system\noptions(press and enter)\n1. Login\n2. signup")
input_username = input('Username: ')
input_password = input('Password: ')

# Everything inside a try ... except block
try:
    # If choice is not 1 and not 2 then error out.
    # You could build a looping mechanism here for retries
    if user_choice != '1' or user_choice != '2':
        raise Exception('Invalid choice')

    # Since we know that choice is 1 or 2 and both require username validation
    # and database acces. We can preform this here
    username_exists = usernameExists(input_username)

    # If logging in the username must exist. If it doesn't then we error or do something else
    if user_choice == '1': # Login
        if !username_exists:
            raise Exception('Username does not exist')

        # Login Success

    # For signup we need to have a unique username. If it exists we can't use it.
    elif user_choice == '2': # Signup
        if username_exists:
            raise Exception('Username is already taken')

        # Login Success
        # We can also insert username with password
        insertUser(input_username, input_password)

# All error handling for code under try can be preformed here
except Exception as error:
    print(error.message)