我正在努力讓我的方法正常工作。我考慮過使用lambda我為另一個問題所做的函數并且有效，但是在這里它似乎不起作用。我正在嘗試將函數更改為方法，但由于某種原因，我的方法無法正常工作，因為它沒有引用樹。我嘗試過使用一個lambda函數，盡管它不起作用。我的錯誤：NameError: name 'tree' is not definedException in Tkinter callbackTraceback (most recent call last):  File "/usr/lib/python3.8/tkinter/__init__.py", line 1883, in __call__    return self.func(*args)  File "/home/bitvivaz/Documents/Software Development/Python/PasswordManager/mainFrame.py", line 54, in select    print([tree.item(x) for x in tree.selection()])NameError: name 'tree' is not defined這是我的代碼：import tkinter as tkimport tkinter.ttk as ttkfrom encryption import encrypted_password, decrypt_passwordimport backend as dbdef get_credentials(tree):    '''Retrieves all credentials from the database and inserts it into the tree widget'''    for row in db.show_credentials():        tree.insert("", 'end', text=row['name'], values=(            row['username'], decrypt_password(row['password'])))class MainframeApp:    def __init__(self, master=None):        # build ui        frame_main = ttk.Frame(master)        frame_main.config(height='600', width='600')        frame_main.grid()        # Creates tree widget        tree = ttk.Treeview(frame_main)        tree["columns"] = ("one", "two")        tree.column("#0")        tree.column("one")        tree.column("two")        tree.heading("#0", text="Website")        tree.heading("one", text="Username")        tree.heading("two", text="Password")        tree.grid(padx='5', pady='5', rowspan='20')        get_credentials(tree)        tree.bind("<<TreeviewSelect>>", self.select, "+")        button_add = ttk.Button(frame_main)