[Tkinter-discuss] 回复： get root.winfo_pointerxy()

[守株待兔]

in my program,myprint is:

def  myprint(arg):
    x=arg.x
    y=arg.y
    canvas.create_text(x,y,text='i am here')
    

canvas.bind("<Button-1>",myprint)

now ,when i left click mouse  on the point in then canvas first time, there is output: i am here
when i left click mouse  on the point in then canvas  second time,there is output too:i am here

what i want to get is :
when i left click mouse  on the point in then canvas  second time,the old  output (i am here) disappear,
only new output (i am here)  in the canvas,how to do ?
any advice  appreciated. 
------------------ 原始邮件 ------------------
发件人: "Cameron Laird"<Cameron at phaseit.net>;
发送时间: 2011年9月1日(星期四) 晚上11:19
收件人: "Douglas S. Blank"<dblank at cs.brynmawr.edu>; 
抄送: "tkinter-discuss"<tkinter-discuss at python.org>; 
主题: Re: [Tkinter-discuss] get  root.winfo_pointerxy()

 
On Thu, Sep 01, 2011 at 10:37:31AM -0400, Douglas S. Blank wrote:
			.
			.
			.
> On 09/01/2011 10:21 AM,         wrote:
> >def  myprint():
> >     print  root.winfo_pointerxy()
> >
> >canvas.bind("<Button-1>",myprint)
> 
> When you bind a function to the canvas, it is expecting a function that 
> takes an argument (which is probably the object to which the binding  is 
> bound).
> 
> So, you could just allow myprint to take an argument, and ignore it:
> 
> def  myprint(arg):
>      print  root.winfo_pointerxy()
			.
			.
			.
I entirely agree with the counsel Dr. Blank has provided.
While I expect the original questioner has all he needs to
move forward, I'll provide a bit more detail for the
benefit of other readers.

Let's look at "arg", "which is probably the object to
which the binding is bound".  It's not; it's the detected
*event* (from which that object can be calculated, though)
<URL: http://www.pythonware.com/library/tkinter/introduction/events-and-bindings.htm >.

That's not all.  One could temporarily update myprint's
definition to be something like

  def myprint(arg):
      print "arg is '%s'." % arg
      print dir(arg)
      print root.winfo_pointerxy()

to have Python's introspection report more information
about the argument.  

And *that* isn't all, either.  If one were somehow 
stranded-on-a-desert-island and unsure how many (not-
necessarily-named) arguments were arriving, one could
experiment with

    def myprint(*kw):
	print kw
	  ...
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