Finance (buy) having trouble to update the table

Question

So I'm trying to update the "share" column in an existing row in the table portfolio instead of creating a new one when buying a stock that the user already has, here is my code:

def buy():
    """Buy shares of stock"""
    if request.method == "POST":
        symbol = request.form.get("symbol")
        n_shares = request.form.get("share")

        if int(n_shares) < 1:
            return apology("Buy at least one", 403)

        quote = lookup(symbol)
        if quote == None:
            return apology("Stock not found", 403)

        chart_value = quote["price"] * int(n_shares)
        stock_name = quote["name"]
        stock_price = quote["price"]
        current_cash = user_cash()

        if current_cash < int(chart_value):
            return apology("Can't afford it", 403)

        update_cash = round(current_cash - chart_value)
        date = datetime.datetime.now()
        date_format = date.strftime("%d-%m-%y %H:%M:%S")

        # Update database

        # Select table portfolio
        rows = ("SELECT * FROM portfolio WHERE user_id = ?", session["user_id"])

        # Check if portfolio is empty
        if len(rows) == 0:
            db.execute("INSERT INTO portfolio (name, symbol, price, share, user_id) VALUES (?, ?, ?, ?, ?)", stock_name, symbol, stock_price, n_shares, session["user_id"])
        
        # If user don't have stocks for that company, insert new row
        elif symbol not in rows:
            db.execute("INSERT INTO portfolio (name, symbol, price, share, user_id) VALUES (?, ?, ?, ?, ?)", stock_name, symbol, stock_price, n_shares, session["user_id"])
        
        # If user have stocks for that company, update it's number of shares
        else:
            stock1 = db.execute("SELECT symbol, stock_id FROM portfolio WHERE name = ? AND user_id = ?", stock_name, session["user_id"])
            stock1_symbol = stock1[0]["symbol"]
            stock1_id = stock1[0]["stock_id"]
            if symbol == stock1_symbol:
                db.execute("UPDATE portfolio SET share = share + ? WHERE user_id = ? AND stock_id = ?", n_shares, session["user_id"], stock1_id)

        db.execute("INSERT INTO history (name, symbol, price, share, date, user_id) VALUES (?, ?, ?, ?, ?, ?)", stock_name, symbol, stock_price, n_shares, date_format, session["user_id"])
        db.execute("UPDATE users SET cash = ? WHERE id = ?", update_cash, session["user_id"])

        return redirect("/")
    else:
        return render_template("buy.html")

I tried a lot of different versions of the code. This version inserts a new row instead of update it. As I could see, the command elif symbol not in rows: can't figure out that that symbol exists in rows and it inserts a new line. I don't know why. In another version, I managed to update an existing row, but it didn't insert a new one if the user didn't have it yet in the portfolio. Can anyone help me?

--EDIT--

I updated my code to this from rows = down:

rows = ("SELECT * FROM portfolio WHERE user_id = ? AND symbol = ?", session["user_id"], symbol)
        if len(rows) != 0:
            stock1 = db.execute("SELECT symbol, stock_id FROM portfolio WHERE name = ? AND user_id = ?", stock_name, session["user_id"])
            stock1_id = stock1[0]["stock_id"]
            db.execute("UPDATE portfolio SET share = share + ? WHERE user_id = ? AND stock_id = ?", n_shares, session["user_id"], stock1_id)

        else:
            db.execute("INSERT INTO portfolio (name, symbol, price, share, user_id) VALUES (?, ?, ?, ?, ?)", stock_name, symbol, stock_price, n_shares, session["user_id"])

But still not solved the problem. Even when the user don't have the stock in portfolio, it's running the command if len(rows) != 0:, so I'm guessing that the query for rows is not returning empty as it should.

--2nd EDIT--

Now my code look like this:

    stockid = db.execute("SELECT stock_id FROM portfolio WHERE symbol = ? AND user_id = ?", symbol, session["user_id"])

        if len(stockid) != 0:
            s_id = stockid[0]["stock_id"]
            db.execute("UPDATE portfolio SET share = share + ? WHERE user_id = ? AND stock_id = ?", n_shares, session["user_id"], s_id)

        else:
            db.execute("INSERT INTO portfolio (name, symbol, price, share, user_id) VALUES (?, ?, ?, ?, ?)", stock_name, symbol, stock_price, n_shares, session["user_id"])

And it works fine.

Answer 1

elif symbol not in rows: will always return True becauserows is a list of dictionaries, and symbol is a string. You could iterate through rows and check the value of each row['symbol'] against symbol.

--OR--

Think about how the function would work if this:

rows = ("SELECT * FROM portfolio WHERE user_id = ?", session["user_id"])

is replaced with [line break added for reading clarity]:

rows = ("SELECT * FROM portfolio WHERE user_id = ? and 
    symbol = ?", session["user_id"],symbol)

Now it knows whether user holds this stock or not.

--EDIT--

If rows is the empty list, insert a record, otherwise do the arithmetic and update the existing record. There are only two conditions.