PSET9 Finance: USD function returns error only when both rendering Index AND after BUY completes a 'purchase'

Question

"unsupported format string passed to Undefined.format"--I know this happens because the non-numerical value is passed into the USD function, but I can't seem to spot the culprit.

As mentioned, index.html (and USD) works fine if accessed at any time NOT after buy is execute.

def index():
    userid = session["user_id"]
    """Show portfolio of stocks"""
    # Calculate the sum cash value of each share holding and update it in PORTFOLIO
    cash_dict = db.execute("SELECT cash FROM users WHERE id = ?", session["user_id"])
    owned_stocks = db.execute("SELECT symbol, name, price, sum(shares) AS sum_shares, price FROM portfolio WHERE id = ? GROUP BY symbol", userid)
    if not owned_stocks:
        return apology("Portfolio Empty", 400)
    cash_one = cash_dict[0]["cash"]
    cash = int(cash_one)

    # Declare the stock+cash variable since declaring it inside the Python for loop will limit the variable scope to inside the for loop
    total = int(cash)

    # Calculate total values of stocks and cash - multiplying the total value of a particular share by its price and pre-adding user's cash ammount
    for stock in owned_stocks:
        total += int(stock["price"]) * stock["sum_shares"]

    return render_template("index.html", owned_stocks=owned_stocks, cash=int(cash), total=int(total))


*******************

def buy():
    """Buy shares of stock"""
    userid = session["user_id"]
    if request.method == "POST":
        symbol = request.form.get("symbol").upper()
        # Ensure user input symbol
        if not symbol:
            return apology("Symbol No No")
        # Get stock price
        lookup_dict = lookup(symbol)
        # Valid symbol?
        if not lookup_dict:
            return apology("Symbol doesn't exist")
        # Stock price, name, and symbol
        stock_price = lookup_dict["price"]
        stock_symbol = lookup_dict["symbol"]
        stock_name = lookup_dict["name"]

        # Get shares number and convert to int, use an exception in case of error
        try:
            shares = int(request.form.get("shares"))
        except:
            return apology("Enter integer only")
        # Ensure int is positive and not zero
        if shares <= 0:
            return apology("Positive number only")
        # Get shares total price
        total_price = shares * stock_price
        # How much CASH user has?
        cash_dict = db.execute("SELECT cash FROM users WHERE id = ?", userid)
        # Since db.execute returns a LIST OF DICTS, I'll extract the int value from it
        cash = cash_dict[0]['cash']
        # Can user afford to buy the stocks?
        if cash < total_price:
            return apology("Not enough cash")
        # Cash spent
        current_cash = cash - total_price
        print("!!!!!!!")
        print(current_cash)
        # Update USERS to reflect cash transaction
        db.execute("UPDATE users SET cash = ? WHERE id = ?", current_cash, userid)
        # Update PORTFOLIO
        db.execute("INSERT INTO portfolio (user_id, symbol, shares, buy_or_sell, name, price) VALUES (?,?,?,?,?,?)", userid, symbol, shares, "purchase", stock_name, stock_price)

        return render_template("index.html")

    return render_template("buy.html")

*****************************
{% extends "layout.html" %}

{% block title %}
Index
{% endblock %}

{% block main %}

<table class="table table-striped">
  <thead>
    <th>Symbol</th>
    <th>Name</th>
    <th>Number of Shares</th>
    <th>Price</th>
    <th>TOTAL</th>
  </thead>
  <tbody>
    {% for stock in owned_stocks %}
    <tr>
      <td>{{ stock["symbol"] }}</td>
      <td>{{ stock["name"] }}</td>
      <td>{{ stock["sum_shares"] }}</td>
      <td>{{ stock["price"] | usd }}</td>
      <!--multiply total number of each particular share by its price for each shares total stocks value!-->
      <td>{{ (stock["sum_shares"] * stock["price"]) | usd }}</td>
    </tr>
    {% endfor %}
    <tr>
      <td colspan="4">Cash</td>
      <td>{{ cash | usd }}</td>
    </tr>
  <tfoot>
    <td colspan="4"></td>
    <td> <strong> Grand Total: {{ total | usd }} </strong> </td>
  </tfoot>
  </tbody>
</table>
{% endblock %}