Doing cs50 Finance and "buy" is generating a run time error - cs50

Question

My error is where I adjust cash to reflect the purchase of stock. The command line error is: RuntimeError: near "['user_id']": syntax error. I have used both " " and ' ' correctly within the line of code. Also further up in command line I got: ERROR: Exception on /buy [POST], which I don't understand. Please let me know if you have any thought. Thanks.
#app.route("/buy", methods=["GET", "POST"])
#login_required
def buy():
"""Buy shares of stock"""
if request.method == "POST":
# Ensure ticker was submitted
if not request.form.get("symbol"):
return apology("must input stock symbol")
# Get symbol and make sure it exists
symbol = lookup(request.form.get("symbol"))
if not symbol:
return apology("symbol does not exist")
# Ensure shares entered greater than zero
number=int(request.form.get("shares"))
if number <= 0:
return apology("must enter number of shares to buy")
# set up dict to store purchase info: name, price, symbol
quote = lookup(request.form.get("symbol"))
# Dollars needed for purchase
pcash=number * quote["price"]
# Is there enough cash in account to purchase
ecash = db.execute("SELECT cash FROM users WHERE id = ?", session["user_id"])
if pcash >= ecash[0]["cash"]:
return apology("Not enough cash to buy that amount of stock")
# Record buy in trades.db for user-id
x=datetime.datetime.now()
db.execute("INSERT INTO trades (datetime, symbol, shares, price, total, id) VALUES(?, ?, ?, ?, ?, ?)", x, quote["symbol"], number, quote["price"], pcash, session["user_id"])
# Adjust cash to reflect purchase
y=ecash[0]["cash"]-pcash
db.execute("UPDATE users SET cash=? WHERE id=session['user_id']", y)
# Redirect user to home page
return redirect("/")
# User reached route via GET (as by clicking a link or via redirect)
else:
return render_template("buy.html")

Answer 1

This UPDATE users SET cash=? WHERE id=session['user_id'] is the query that sqlite is trying to execute. sqlite doesn't know from session['user_id'] (it's a python variable). The method will accept multiple placeholders (ie ?). Use a placeholder for the WHERE clause, and send the value as an additional argument.