app.py

@app.route("/user/<int:id>", methods=["GET"])
def get_user_by_id(id):
    user = User.query.filter_by(id=id).first()
    if not user:
        return jsonify({"message": "Not user found."}), 404
    else:
        user_data = {}
        user_data["id"] = user.id
        user_data["username"] = user.username
        user_data["admin"] = user.admin
    return jsonify({"user": user_data}), 200