signup.py

import os


def Signup():
    print('===Signup===\n')

    # To Ask and check username, if exists ask again
    while True:
        uname = input('Username: ')
        fname = uname + '.dat'
        if not ' ' in uname:
            if os.path.exists(fname):
                print('User already exists, pls try another Username!')
                continue

            else:
                break
        else:
            print('SPACE in Username, please try again!')
            continue

    # To Ask password and check it
    while True:
        password = input('Password: ')
        confirm_password = input('Confirm Password: ')
        if password == confirm_password:
            break
        else:
            print('Passwords do not match, pls try again!')

    # Open file and Save password
    file = open(fname, 'w')
    file.write(password)
    file.close()
    print(f'Signup user {uname} Successfully')


def Signin():
    print('===Signin===\n')
    uname = input('Username: ')
    password = input('Password: ')
    fname = uname + '.dat'

    # check if username is OK
    if not os.path.exists(fname):
        print(f'Username {uname} does not exists')
        ans = input('Signup? (y\\n): ')
        if ans.lower() == 'y':
            Signup()
        else:
            exit()
    # check if password is OK
    else:
        file = open(fname, 'r')
        password_in_file = file.read().rstrip()
        file.close()
        if password == password_in_file:
            print('Signin Successfully...')
            # Call fun from here
        else:
            print('wrong password,exiting...')


# Program Start Here
if __name__ == '__main__':
    Signin()