cs50 金融项目：lookup() 不返回字典

Question

在实现

buy()

函数时，我需要使用从

lookup(symbol)

中找到的

helpers.py

函数返回的字典，并在

app.py

中访问它。但它似乎没有返回任何数据。代码如下。

# in helper.py

   """
   Decorate routes to require login.
   https://flask.palletsprojects.com/en/1.1.x/patterns/viewdecorators/
   """
   @wraps(f)
   def decorated_function(*args, **kwargs):
       if session.get("user_id") is None:
           return redirect("/login")
       return f(*args, **kwargs)
   return decorated_function


def lookup(symbol):
   """Look up quote for symbol."""

   # Contact API
   try:
       api_key = os.environ.get("API_KEY")
       response = requests.get(f"https://cloud-sse.iexapis.com/stable/stock/{urllib.parse.quote_plus(symbol)}/quote?token={api_key}")
       response.raise_for_status()
   except requests.RequestException:
       return None

   # Parse response
   try:
       quote = response.json()
       return {
           "name": quote["companyName"],
           "price": float(quote["latestPrice"]),
           "symbol": quote["symbol"]
       }
   except (KeyError, TypeError, ValueError):
       return None

app.py中的代码是

def buy():
    if request.method == "GET":
        return render_template("buy.html")

    else:
        symbol = request.form.get("symbol")
        shares = request.form.get("share_num")
        result = lookup(symbol)


        cash = db.execute("SELECT cash FROM users WHERE id = ?", session["user_id"])
        if cash < result["price"] * request.form.get("share_num"):
            return apology("insufficient balance",403)
        db.execute("INSERT INTO stock(symbol,name,quantity,price) VALUES (?,?,?,?) WHERE users.id = stock.user_id AND id= ?",
                   result["symbol"], result["name"], request.form.get("share_num"),result["price"],session["user_id"])
        db.execute("UPDATE users(cash) SET (?) WHERE users.id = stock.user_id AND id=? ",
                   cash - result["price"] * request.form.get("share_num"), session["user_id"])
        return redirect("/")

html代码是

{% block title %}
    buy stock
{% endblock %}

{% block main %}
    <form action="/buy" method="post">
        <div class="mb-3">
            <input autocomplete="off" autofocus class="form-control mx-auto w-auto"  name="symbol" placeholder="symbol" type="text">
        </div>
        <div class="mb-3">
            <input class="form-control mx-auto w-auto" name="share_num" placeholder="quantity" type="number">
        </div>
        <button class="btn btn-primary" type="submit">buy</button>
    </form>
{% endblock %}

我得到的错误是

File "/workspaces/89966944/finance/helpers.py", line 33, in decorated_function
return f(*args, **kwargs)
       ^^^^^^^^^^^^^^^^^^
File "/workspaces/89966944/finance/app.py", line 64, in buy
  if cash < result["price"] * request.form.get("share_num"):
          ~~~~~~^^^^^^^^^
TypeError: 'NoneType' object is not subscriptable