我换了一个邮箱，重新发看看

> from Tkinter import *
> 
> root = Tk()
> 
> frame = Frame(root, width=200, height=250)
> 
> def callback(event):
> global x,y
> x = event.x
> y = event.y
> #print x, y
> 
> c = x - a;d = y - b
> 
> if abs(c) >= 3 or abs(d) >= 3:
> print c, d
> a = a + c; b = b + d
> print a, b
> 
> def callback1(event):
> global a,b
> a = event.x
> b = event.y
> print a, b
> 
> frame.bind("<1>", callback1)
> frame.bind("", callback)
> 
> frame.pack()
> 
> root.mainloop()
> 

a,b是在callback1(event)中定义的全局变量，取的是鼠标点击时的坐标值。必然先点击左键，才有按住左键拖动，所以a,b必然会在x,y前被定义赋值.
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> 
> 你应该在main()中或者 if __name__ == '__main__' 
> 中定义global变量,或者在callback()中重新global一次.
>
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lveax wrote:
> 我换了一个邮箱，重新发看看
[...]
>     def callback(event):
>         global x,y
>         x = event.x
>         y = event.y
>         #print x, y
> 
>         c = x - a;d = y - b
> 
>         if abs(c) >= 3 or abs(d) >= 3:
>           print c, d
>           a = a + c; b = b + d
>           print a, b
[...]

嗯，这次有缩进，就容易看多了。

你在callback()里有这样的语句：
a = a + c; b = b + d
这句语句对a和b进行赋值，你前面又没有定义global a, b，因此python认为本函
数内的a、b为局部名字。

没仔细看你的代码，如果你这里是想改变全局的a和b，那么在callback()里加上
global a, b
如果不是，那就改两个名字好了。

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Qiangning Hong
http://www.hn.org/hongqn (RSS: http://feeds.feedburner.com/hongqn)

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