from flask import Flask, request

app = Flask(__name__)

users = {}

@app.route('/')
def a():
    return '''
    <form action="/l">
    ID: <input name="u"><br><br>
    Password: <input name="p"><br><br>
    <input type="submit">
    </form>
    '''

@app.route('/l')
def b():
    u = request.args.get('u')
    p = request.args.get('p')

    if u not in users:   # only new user
        users[u] = p

        for i in users:
            print("id:", i, "password:", users[i])
        print("total =", len(users))
        print("--------")

        return "User Added"
    else:
        return "User Already Exists"

if __name__ == "__main__":
    app.run()