如何通过add_command的command参数修改值？用Lambda实现Tkinter文件存变量

1. Can we modify a value using add_command's command parameter? #

Yes, you can. The command parameter accepts any callable, so lambda functions can be used to modify variables in the surrounding scope:

• For mutable types (lists, dictionaries, Tkinter variables like StringVar), you can alter their contents directly in the lambda.
• For immutable types (strings, integers), wrap them in a mutable container (like a single-element list) or use nonlocal/global keywords if the variable is in an outer function or global scope.

2. Saving file path to a variable using only lambda functions #

Your current code triggers the file dialog but doesn't store the selected path. You can fix this by using a mutable variable to hold the path, then assigning the dialog's result to it inside a lambda. Here are two working approaches:

Approach 1: Using a list (simple mutable container) #

from tkinter import tk
from tkinter.filedialog import askopenfilename

root = tk.Tk()
controlMenuBox = tk.Menu(root)

# Mutable list to store the file path
selected_path = []

openFile = lambda initial_dir, title, file_types: askopenfilename(
    initialdir=initial_dir, title=title, filetypes=file_types
)

fileMen = tk.Menu(controlMenuBox, tearoff=0)
controlMenuBox.add_cascade(label='File', menu=fileMen)
# Lambda assigns the selected path to the list (overwrites if already exists)
fileMen.add_command(
    label='Open File',
    command=lambda: selected_path.__setitem__(0, openFile("/", "Open File", (("Text files", "*.txt"), ("all files", "*.*")))) if selected_path else selected_path.append(openFile("/", "Open File", (("Text files", "*.txt"), ("all files", "*.*"))))
)

# Optional: Add a button to verify the stored path
def show_path():
    if selected_path:
        print(f"Selected path: {selected_path[0]}")
tk.Button(root, text="Show Selected Path", command=show_path).pack()

homeMenu = tk.Canvas(root, width=800, height=600, bg="#fff7e8")
homeMenu.pack()

root.config(menu=controlMenuBox)
root.mainloop()

Approach 2: Using Tkinter's StringVar (idiomatic for GUI apps) #

This is better if you want to bind the path directly to GUI elements like labels:

from tkinter import tk
from tkinter.filedialog import askopenfilename

root = tk.Tk()
controlMenuBox = tk.Menu(root)

# Tkinter mutable string variable to store the path
selected_path = tk.StringVar()

openFile = lambda initial_dir, title, file_types: askopenfilename(
    initialdir=initial_dir, title=title, filetypes=file_types
)

fileMen = tk.Menu(controlMenuBox, tearoff=0)
controlMenuBox.add_cascade(label='File', menu=fileMen)
# Lambda uses StringVar's set method to store the path
fileMen.add_command(
    label='Open File',
    command=lambda: selected_path.set(openFile("/", "Open File", (("Text files", "*.txt"), ("all files", "*.*"))))
)

# Optional: Display the path in a label
tk.Label(root, text="Selected Path:", font=("Arial", 10)).pack()
tk.Label(root, textvariable=selected_path, fg="blue", font=("Arial", 10)).pack()

homeMenu = tk.Canvas(root, width=800, height=600, bg="#fff7e8")
homeMenu.pack()

root.config(menu=controlMenuBox)
root.mainloop()

Both solutions avoid regular functions and use lambdas exclusively to capture and store the file path. The core idea is using a mutable variable so the lambda can modify its value without needing a separate function definition.

内容的提问来源于stack exchange，提问作者Tech Zachary ZN