TypeError: 'NoneType' object is not subscriptable in PSET9, but working manually

Question

I am working on pset9 Finance. I have implemented the functionality for purchasing stocks, and it works well when I manually test it. However, when I run the CS50's check50 validation, it returns an error: "exception raised in application: TypeError: 'NoneType' object is not subscriptable" on the ":( buy handles valid purchase" validation.

I have checked my code thoroughly and cannot identify the source of this issue. The error message suggests that I am trying to access an element of a NoneType object using subscript notation, but I cannot reproduce the error when I manually test the functionality.

I have reviewed my code and ensured that I handle potential None values properly. I also checked the data types and made sure that the necessary data is provided before accessing it.

I am seeking guidance on how to troubleshoot this issue further and understand why it fails during the check50 validation but not during manual testing. Any insights or suggestions on what I may be overlooking would be greatly appreciated.

Also, this question was written by ChatGPT, because it is after midnight and I have been trying to figure it out for hours now.

Here is my python/flask code

@app.route("/buy", methods=["GET", "POST"])
@login_required
def buy():
    """Buy shares of stock"""
    if request.method == "GET":
        return render_template("purchase.html")

    elif request.method == "POST":
        # Check for missing values
        if not request.form.get("symbol"):
            return apology("Enter stock symbol i.e. NFLX", 400)
        elif not request.form.get("shares"):
            return apology("Enter amount of stock", 400)

        # Check for numbers
        if request.form.get("shares").isdecimal() == False:
            return apology("Enter a number", 400)

        # Check for decimal
        if "," in request.form.get("shares") or "." in request.form.get("shares"):
            return apology("Cannot buy fractional", 400)

        # Get stock dictionary
        quote = request.form.get("symbol")
        amount = int(request.form.get("shares"))

        # Check for invalid symbol
        if lookup(quote) == None:
            return apology("Enter stock symbol i.e. NFLX", 400)

        stock = lookup(quote)

        # Check for negative number
        if amount <= 0:
            return apology("Enter positive number", 400)

        # Check for funds
        price = (float(stock["price"]) * float(amount))
        funds = db.execute("SELECT cash FROM users WHERE id = ?", session["user_id"])
        funds = float(funds[0]["cash"])

        if funds < price:
            return apology("insufficient funds", 400)

        date = datetime.now()
        # Add purchase into database
        db.execute("INSERT INTO stocks (stock, amount, date_time, buyer_id) VALUES (?, ?, ?, ?);", stock["name"], amount, date, session["user_id"])

        # Add purchase into transaction
        db.execute("INSERT INTO transactions (stock, amount, type, date_time, buyer_id) VALUES (?, ?, ?, ?, ?);", stock["name"], amount, 'buy', date, session["user_id"])

        # Reduce funds
        funds = funds - price
        db.execute("UPDATE users SET cash = ? WHERE id = ?", funds, session["user_id"])

        return redirect("/")
    else:
        return apology("Unknown error") # Just in case

---

And here is my HTML code:

{% extends "layout.html" %}

{% block title %}
    Buy
{% endblock %}

{% block main %}
    <form action="/buy" method="post">
        <div class="mb-3">
            <input autocomplete="on" autofocus class="form-control mx-auto w-auto" id="symbol" name="symbol" placeholder="Stock symbol" type="text" required>
        </div>
        <div class="mb-3">
            <input autocomplete="on" autofocus class="form-control mx-auto w-auto" id="shares" name="shares" placeholder="Stock amount" type="number" min="1" required>
        </div>
        <button class="btn btn-primary" type="submit">Buy stock</button>
    </form>
{% endblock %}

Can you give me a hand, please? Thanks very much!

Answer 1

I noticed that the issue lies in the line where I insert the stock symbol into the "stocks" table in the buy function. The problem is that I am passing stock["name"] instead of stock["symbol"].

The correct code would be

db.execute("INSERT INTO stocks (stock, amount, date_time, buyer_id) VALUES (?, ?, ?, ?);", stock["symbol"], amount, date, session["user_id"])

Answer 2

I had the exact same problem and spent 4hrs trying to find the issue without success until I found this post. Thank you so much!