主窗口已存在但Combobox仍抛出错误的问题求助

各位大佬，我正在开发一个基于ttkbootstrap的股票交易模拟器GUI，现在遇到了一个奇怪的问题：明明主窗口main_window已经创建完成，但我的Combobox组件还是抛出了“找不到主窗口”相关的错误（抱歉没把完整错误信息贴出来，核心问题就是组件无法关联到已创建的主窗口）。

以下是我目前的完整代码，麻烦帮忙排查一下问题出在哪：

import ttkbootstrap as ttk
from random import choice, choices
import csv
from Login import Login
login = Login()
login.login_gui()
user = login.authenticated_user
if user:
    with open('tanishStock_data.csv') as sheet:
        reader = list(csv.DictReader(sheet))
        day = int(reader[-1]['Day'])
        cash = float(reader[-1]['Cash'])
        stocks = {"reliance":float(reader[-4]['Price']), "tata motors":float(reader[-3]['Price']), "itc":float(reader[-2]['Price']), "mahindra":float(reader[-1]['Price'])}
    labels = {} #stores stock_name:it's price_label (refer to line 108)
    holdings = {} #stock : {quantity, price, value}
    def update_label(label, text, fg=None):
        label.configure(text=text, foreground = fg)
    portfolio_window = None
    def bull_run(stock):
        inc_or_dec = choices([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], weights=[20, 30, 10, 8, 7, 4, 3, 2, 2, 1])[0]
        stocks[stock] = stocks[stock] * inc_or_dec / 100 + stocks[stock]
    def bear_run(stock):
        inc_or_dec = choices([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], weights=[20, 30, 10, 8, 7, 4, 3, 2, 2, 1])[0]
        stocks[stock] = stocks[stock] - stocks[stock] * inc_or_dec / 100
    def simulate_stocks():
        for stock in stocks:
            randomizer = choice(["plus", "minus"])
            if randomizer == "plus":
                bull_run(stock)
            elif randomizer == "minus":
                bear_run(stock)
            else:
                print("error encountered")
                break
        update_prices()
        main_window.after(5000, simulate_stocks)
    def update_prices():
        for stock_name, label in labels.items():
            price = float(label.cget("text")) #gets the price out of the price_label
            if price > stocks[stock_name]:
                update_label(label, f"{stocks[stock_name]:.2f}", fg = "red")
            else:
                update_label(label, f"{stocks[stock_name]:.2f}", fg = "#228B22")
    def buy_stock():
        global cash
        stock = vvariable.get().strip().lower()
        try:
            quantity = int(entry_quantity_price.get())
        except ValueError:
            update_label(quantity_warning, "*Enter a valid quantity")
            return
        if stock in stocks:
            total_cost = quantity * stocks[stock]
            if total_cost > cash:
                update_label(quantity_warning, "*Not enough cash")
            elif quantity <= 0 or quantity > 10000:
                update_label(quantity_warning,"*Quantity should be between 1 and 10000")
            else:
                update_label(quantity_warning, "")
                update_label(stock_warning, "")
                if stock not in holdings:
                    holdings[stock] = {"quantity": 0, "price": 0, "value": 0}
                holdings[stock]["price"] = (stocks[stock] * quantity + holdings[stock]["price"] * holdings[stock]["quantity"])/(quantity + holdings[stock]["quantity"])
                holdings[stock]["quantity"] += quantity
                holdings[stock]["value"] = holdings[stock]["quantity"] * holdings[stock]["price"]
                cash -= total_cost
                update_label(cash_display, f"CASH: {cash:.2f}")
        else:
            update_label(stock_warning, "*No such stock exists")
    def sell_stock():
        global cash
        stock = vvariable.get().strip().lower()
        try:
            quantity = int(entry_quantity_price.get())
        except ValueError:
            update_label(quantity_warning, "*Enter a valid quantity")
            return
        if stock in holdings:
            if quantity <= 0 or quantity > holdings[stock]["quantity"]:
                update_label(quantity_warning, "*Invalid quantity")
            else:
                update_label(quantity_warning, "")
                update_label(stock_warning, "")
                holdings[stock]["quantity"] -= quantity
                sell_value = quantity * stocks[stock]
                cash += sell_value
                update_label(cash_display, f"CASH: {cash:.2f}")
                holdings[stock]["value"] = holdings[stock]["quantity"] * holdings[stock]["price"]
                if holdings[stock]["quantity"] == 0:
                    del holdings[stock]
        else:
            stock_warning.config(text="*You don't own this stock")
    def stock_data_writer(real_day): # writes stock data in csv file
        with open('tanishStock_data.csv', mode ='a', newline ='') as sheet:
            writer = csv.DictWriter(sheet, fieldnames = ['Day', 'Stock', 'Price', 'Cash'])
            for stock in stocks:
                writer.writerow({'Day' : real_day, 'Stock' : stock, 'Price' : f'{stocks[stock]:.2f}', 'Cash' : f'{cash:.2f}'})
    def day_system(): #manages day system in the stock simulator
        global day
        day += 1
        stock_data_writer(day)
        update_label(day_display, text = f"DAY : {day}", fg = "red")
        main_window.after(20000, lambda: day_system())
    def clickable_stocks(stockname, stockprice):
        entry_stock_entry.delete(0, ttk.END)
        entry_quantity_price.delete(0, ttk.END)
        entry_stock_entry.insert(0, stockname)
        entry_quantity_price.insert(0, stockprice)
    def show_portfolio():
        global portfolio_window

        # Destroy the existing portfolio window if it exists
        if portfolio_window:
            portfolio_window.destroy()

        # Create new portfolio window
        portfolio_window = ttk.Toplevel(main_window)
        portfolio_window.title("PORTFOLIO")
        portfolio_window.geometry("420x300")
        portfolio_window.resizable(False, False)

        # Create canvas and scrollbar
        canvas = ttk.Canvas(portfolio_window)
        scrollbar = ttk.Scrollbar(portfolio_window, orient="vertical", command=canvas.yview)
        canvas.configure(yscrollcommand=scrollbar.set)

        # Create a frame inside the canvas
        canvas_frame = ttk.Frame(canvas)
        canvas.create_window((0, 0), window=canvas_frame, anchor="nw")

        # Pack the scrollbar and canvas
        scrollbar.pack(side="right", fill="y")
        canvas.pack(side="left", fill="both", expand=True)

        def update_portfolio_window():
            # Clear the frame before updating
            for widget in canvas_frame.winfo_children():
                widget.destroy()
            row_num = 2
            cash_label = ttk.Label(canvas_frame, text=f"CASH: {cash:.2f}", font=("arial", 13, "bold"),foreground="green")
            cash_label.grid(row=0, column=0, padx=10, pady=10, sticky="w")
            upper_divider = ttk.Label(canvas_frame, text="_" * 80)
            upper_divider.grid(row=1, column=0, columnspan=2, padx=10)
            if holdings:
                for stock, data in holdings.items():
                    stock_name = ttk.Label(canvas_frame, text=stock.title(), font=("arial", 15))
                    purchase_data = ttk.Label(canvas_frame,
                                              text=f"Qty: {data['quantity']} | Price: {data['price']:.2f}",
                                              font=("arial", 8))
                    current_value = ttk.Label(canvas_frame, text=f"Value: {data['value']:.2f}", font=("arial", 13),foreground="green")
                    stock_name.grid(row=row_num, column=0, padx=10, pady=5, sticky="w")
                    purchase_data.grid(row=row_num + 1, column=0, padx=10, sticky="w")
                    current_value.grid(row=row_num + 1, column=1, padx=10, sticky="e")

                    row_num += 3
            else:
                no_holdings_label = ttk.Label(canvas_frame, text="No holdings yet.", font=("arial", 12))
                no_holdings_label.grid(row=row_num, column=0, columnspan=2, pady=50)
            close_button = ttk.Button(canvas_frame, text="Close", command=portfolio_window.destroy)
            close_button.grid(row=row_num + 1, column=1, sticky="e", padx=10, pady=10)
            canvas_frame.update_idletasks()
            canvas.config(scrollregion=canvas.bbox("all"))
        update_portfolio_window()
    main_window = ttk.Window(themename = "darkly")


    def on_destroy():
        print("Main window is being destroyed.")
        main_window.destroy()


    main_window.protocol("WM_DELETE_WINDOW", on_destroy)

    main_window.geometry("600x500")
    main_window.title("Tanish Stock Exchange")
    vvariable = ttk.StringVar()
    header = ttk.Label(main_window, text = "TSE", font=("arial", 20), foreground="blue")
    header.pack()
    day_display = ttk.Label(main_window, text = f"DAY : {day}", font = ("arial", 15), foreground='red')
    day_display.place(x = 260, y = 300)
    y_position = 80
    stock_entry = ttk.Label(main_window, text ="STOCK: ", font=("arial", 15, "bold"))
    stock_entry.place(x = 300, y = 80)
    stock_warning = ttk.Label(main_window, text = "", font=("arial", 7), foreground="red")
    stock_warning.place(x = 400, y=110)
    stock_quantity = ttk.Label(main_window, text ="quantity: "

备注：内容来源于stack exchange，提问作者user28243057