无法调用按钮命令：应用程序已被破坏

下面给出了使用 Tkinter 和 Python 创建独立窗口的代码：

import Tkinter

Tkinter.NoDefaultRoot()

win1=Tkinter.Tk()
win2=Tkinter.Tk()

Tkinter.Button(win1, text='Woho!',command=win1.destroy()).pack()
Tkinter.Button(win2, text='Woho!',command=win2.destroy()).pack()

win1.mainloop()

执行时显示：

Traceback (most recent call last):
  File "C:\Users\Administrator\Desktop\eclipse\Python Projects\Project 1\Source1\mod.py", line 8, in <module>
    Tkinter.Button(win1, text='Woho!',command=win1.destroy()).pack()
  File "C:\Python27\lib\lib-tk\Tkinter.py", line 2106, in __init__
    Widget.__init__(self, master, 'button', cnf, kw)
  File "C:\Python27\lib\lib-tk\Tkinter.py", line 2036, in __init__
    (widgetName, self._w) + extra + self._options(cnf))
_tkinter.TclError: can't invoke "button" command:  application has been destroyed

我是 Python 新手，因此不明白它的含义。我哪里出错了？

Remove () from win1.destroy() and win2.destroy().

Tkinter.Button(win1, text='Woho!',command=win1.destroy()).pack()
Tkinter.Button(win2, text='Woho!',command=win2.destroy()).pack()
                                                      ^^

它导致win1.destroy方法调用，并使用方法的返回值作为回调，而不是方法本身；导致主窗口在创建按钮之前销毁。

Tkinter.Button(win1, text='Woho!',command=win1.destroy).pack()
Tkinter.Button(win2, text='Woho!',command=win2.destroy).pack()