Tkinter 意外行为
我一直在使用 Tkinter 用 Python 编写一个很长的 GUI。我不明白的一件事是为什么我不能将事件绑定到循环中的小部件。在下面的代码中,如果我手动执行(注释掉代码)但不在 for 循环中执行绑定,则绑定效果很好。我做错了什么吗?
导入 Tkinter
root = Tkinter.Tk()
b1 = Tkinter.Button(root, text="Button 1")
b1.pack()
b1.focus_set()
b2 = Tkinter.Button(root, text="Button 2")
b2.pack()
b3 = Tkinter.Button(root, text="Button 3")
b3.pack()
def up_and_down(*buttons):
for i in range(len(buttons)-1):
buttons[i].bind("<Down>", lambda x: buttons[i+1].focus_set())
for i in range(1, len(buttons)):
buttons[i].bind("<Down>", lambda x: buttons[i-1].focus_set())
'''
buttons[0].bind("<Down>", lambda x: buttons[1].focus_set())
buttons[1].bind("<Down>", lambda x: buttons[2].focus_set())
buttons[1].bind("<Up>", lambda x: buttons[0].focus_set())
buttons[2].bind("<Up>", lambda x: buttons[1].focus_set())
'''
up_and_down(b1, b2, b3)
root.mainloop()
I've been writing a long GUI in Python using Tkinter. One thing that I don't understand is why I can't bind events to widgets in a loop. In the code below, binding works well if I do it manually (commented out code) but not in a for loop. Am I doing something wrong?
import Tkinter
root = Tkinter.Tk()
b1 = Tkinter.Button(root, text="Button 1")
b1.pack()
b1.focus_set()
b2 = Tkinter.Button(root, text="Button 2")
b2.pack()
b3 = Tkinter.Button(root, text="Button 3")
b3.pack()
def up_and_down(*buttons):
for i in range(len(buttons)-1):
buttons[i].bind("<Down>", lambda x: buttons[i+1].focus_set())
for i in range(1, len(buttons)):
buttons[i].bind("<Down>", lambda x: buttons[i-1].focus_set())
'''
buttons[0].bind("<Down>", lambda x: buttons[1].focus_set())
buttons[1].bind("<Down>", lambda x: buttons[2].focus_set())
buttons[1].bind("<Up>", lambda x: buttons[0].focus_set())
buttons[2].bind("<Up>", lambda x: buttons[1].focus_set())
'''
up_and_down(b1, b2, b3)
root.mainloop()
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您的闭包(lambda)没有按照您的预期工作。它们保留对
i
的引用,该引用会随着循环迭代而发生变化,最后来自同一循环的所有 lambda 都引用同一个最后一个按钮。下面是该行为的说明:
Your closures (lambdas) are not working as you expect them to. They keep references to
i
which is mutated as the loop iterates, and in the end all lambdas from the same loop refer to the same single last button.Here's an illustration of the behaviour:
您可以通过以下方式解决该问题:
注意
lambda
闭包的i=i
参数。You can fix the problem with:
Note the
i=i
argument to thelambda
closure.