Tkinter Lambda函数 [英] Tkinter lambda function

问题描述

(如家庭作业"标签所示，这是计算机科学中 big 项目的一部分.)

(As the 'homework' tag indicates, this is part of a big project in Computer Science.)

我正在用tkinter在Python中编写一个 Jeopardy！模拟，对于在按钮中使用lambda函数，我遇到了一个大问题.假设root = Tk()和categories是一个列表.

I am writing a Jeopardy! simulation in Python with tkinter, and I'm having a big problem regarding the use of the lambda function in buttons. Assume root = Tk() and categories is a list.

# Variable to keep the buttons
root._buttons = {}

# Display headers on top of page
for i in range(5):
    # Get category name for display in main window
    name = categories[i]
    b = Label(root, text=fill(name.upper(), 10), width=18, height=3,\
        bg="darkblue", fg="white", font=("Helvetica bold", "", 11))
    b.grid(row=0, column=i)

    # Create list of buttons in that variable (root._buttons)
    btnlist = [None]*5

    # Display individual questions
    for j in range(5):

        # Make a button for the question
        b = Button(root, text="$" + str(200 * (j+1)), width=8, height=1,
            bg="darkblue", fg="orange", font=("Impact", "", 30))
        b.cat = name
        b.value = 200 * (j + 1)
        b.sel = lambda: select(b.cat, b.value)

        # Add callback event to button
        print(b.cat, b.value, b.sel)
        b.config(command=b.sel)

        # Add button to window
        b.grid(row=j+1, column=i)

        # Append to list
        btnlist[j] = b

    root._buttons[categories[i]] = btnlist

有关所有代码，请参见我的小代码查看器(正在建设中) ！)

For all of the code, see my little Code Viewer (under construction!)

问题似乎在lambda: select(b.cat, b.value)出现，因为当我单击板上的任何按钮时，它总是转到板上的最后一个按钮.我尝试了其他方法，不幸的是，所有方法都使用lambda，而且我还没有看到任何不涉及lambda的方法.

It's at lambda: select(b.cat, b.value) where the problem seems to occur, because when I click any button on the board, it always goes to the one last button on the board. I've tried other approaches, unfortunately all using lambda, and I have not seen any approach that does not involve lambda.

推荐答案

更改

lambda: select(b.cat, b.value)

到

lambda b = b: select(b.cat, b.value)

在您的原始代码中，b不是lambda的局部变量；在封闭范围内找到它. for-loop完成后，b保留其最后一个值.这就是lambda函数都使用最后一个按钮的原因.

In your original code, b is not a local variable of the lambda; it is found in enclosing scope. Once the for-loop is completed, b retains it last value. That is why the lambda functions all use the last button.

如果将lambda定义为采用一个具有默认值的参数，则默认值是在定义时确定的(并固定的).现在b是lambda的局部变量，并且在不带参数的情况下调用lambda时，Python会将b设置为默认值，可以根据需要将其设置为各种不同的按钮.

If you define the lambda to take one argument with a default value, the default value is determined (and fixed) at the time the lambda is defined. Now b is a local variable of the lambda, and when the lambda is called with no arguments, Python sets b to the default value which happily is set to various different buttons as desired.

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