import secrets

sessions = {}

def login(user_id):
    token = secrets.token_hex(8)
    sessions[token] = {"user_id": user_id, "cart": []}
    print(f"Cookieを発行: {token}")
    return token

def whoami(token):
    if token in sessions:
        return sessions[token]["user_id"]
    return None

token = login("alice")
print(f"今のユーザー: {whoami(token)}")