Python Tkinter OptionMenu将命令添加到多个OptionMenu [英] Python Tkinter OptionMenu add a command to multiple OptionMenus

问题描述

基本上，我有一系列的OptionMenu循环创建，但当前为空：

Basically I have a series of OptionMenus that are created in a loop, but is currently empty:

option_menu = []
for ii in range(jj):
    option_menu.append([])  
    for ll in range(kk):   
        option_menu[ii].append(OptionMenu(frame,tkinter_text_var[ii][ll],''))

然后在其他地方，我使用复选框来设置值的范围如下：

Then elsewhere I use a checkbox to set the values along the lines of:

for ii in range(jj):
    for ll in range(kk):   
        option_menu[ii][ll]["menu"].add_command(label = name_from_box.get(), command = lambda: tkinter_text_var[ii][ll].set(name_from_box.get()))

这可以正确地填充所有OptionMenu，但是当我在任何OptionMenu中选择一个值时，它只能设置option_menu [jj] [kk]（即最后一个）。

This works to populate all of the OptionMenus properly, but when I select a value in any of the OptionMenus, it only sets option_menu[jj][kk] (i.e. that last one made).

那我做错了什么？

推荐答案

这是一个涉及closur的非常常见问题es。请看以下示例：

This is a very common question involving closures. Look at the following example:

alist = [lambda : x for x in range(10) ]
print (alist[2]()) #9
print (alist[4]()) #9

全部为9。为什么？因为每个lambda函数都引用变量 x 。 x 在循环中的每次迭代中都会更改，但是它们仍然都引用同一对象。

The'll all be 9. Why? Because each lambda function refers to the variable x. x gets changed at every iteration through the loop, but they all still refer to the same object.

解决此问题的一种方法是使用默认参数。默认参数在创建函数时进行评估，而不是在调用函数时进行评估。

One way around this is to use a default argument. Default arguments are evaluated when the function is created, not when it is called.

alist = [lambda y=x: y for x in range(10) ]
print (alist[2]()) #2
print (alist[4]()) #4

（做同一件事的另一种方法涉及 functools.partial ，您有时会看到... ）

(another way to do the same thing involves functools.partial which you'll see sometimes ...)

我经常想说-小心闭包。他们可能会有些棘手。

I often like to say -- "take care with closures". They can be a little tricky.

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