问CS50财务写入数据库问题

EN

@app.route("/buy", methods=["GET", "POST"])
@login_required
def buy():

    if request.method == "POST":
        quote = lookup(request.form.get("symbol"))

        if quote == None:
            return apology("invalid symbol", 400)

        try:
            shares = int(request.form.get("shares"))
        except:
            return apology("shares must be a positive integer", 400)


        if shares <= 0:
            return apology("can't buy less than or 0 shares", 400)

        users= db.execute("SELECT cash FROM users WHERE id= :user_id", user_id=session["user_id"])

        cash_remaining = users[0]["cash"]
        price_per_share = quote["price"]
        total_price = price_per_share * shares
        balance = cash_remaining-total_price
        symbol=quote["symbol"]


        return render_template ("confirmation.html", cash_remaining=cash_remaining, price_per_share=price_per_share, total_price=total_price,shares=shares, symbol=symbol, balance=balance)

    else:
        return render_template ("buy.html")

@app.route("/confirmation", methods=["GET", "POST"])
@login_required
def confirmation():

    if request.method == "POST":


        db.execute("UPDATE users SET cash = cash = :balance WHERE id = :user_id", balance=balance, user_id=session["user_id"])
        db.execute("INSERT INTO transactions (user_id, symbol, shares, price_per_share) VALUES(:user_id, :symbol, :shares, :price_per_share)",
                   user_id=session["user_id"],
                   symbol=request.form.get("symbol"),
                   shares=shares,
                   price_per_share=price_per_share)

        flash ("Bought!")

        return render_template("index.html")
    else:
        return render_template("confirmation.html")

{% extends "layout.html" %}

{% block title %}
    Quote
{% endblock %}

{% block main %}
     <form action="/buy" method="post">
        <div class="form-group">
            <input autocomplete="off" autofocus class="form-control" name="symbol" placeholder="Symbol" type="text" required/>
        </div>
        <div class="form-group">
            <input autocomplete="off" autofocus class="form-control" name="shares" placeholder="Shares Wanted" type="number" min="1" required />
        </div>
        <button class="btn btn-primary" type="submit">Get Price</button>
    </form>
{% endblock %}

{% extends "layout.html" %}

{% block title %}
    Quote
{% endblock %}

{% block main %}
    <form action="/confirmation" method="post">
        <p>Stock Symbol ={{symbol}}</p>
        <p>Shares to be purchased = {{shares}}</p>
        <p>Total Transaction Cost {{total_price | usd}}</p>
        <p>Current Cash = {{cash_remaining | usd}}</p>
        <p>Balance after transaction = {{balance |usd}}</p>
        <button class="btn btn-primary" type="submit">Buy</button>
    </form>

{% endblock %}