update tkinter window

[Chad Netzer]

On Thursday 14 November 2002 13:59, Roger wrote:
> I've been messing with tkinter a little.
> I was trying to just come up with a window that would show the current
> time.
> stealing some code from examples, I came up with:

[snipped]

Here is my quick rewrite which probably does what you want:


from time import localtime, strftime
from Tkinter import *

class myclock(Frame):
   def update_stats(self):
       self.contents.set(strftime("%H:%M:%S",localtime()))
       self.after(self.msecs, self.update_stats)
       return

   def __init__(self, msecs=1000):
      Frame.__init__(self)
      self.msecs=msecs

      self.contents=StringVar()
      self.entry=Entry(textvariable=self.contents)
      self.entry.pack()

      self.update_stats()
      return

m = myclock( msecs=1000 )
m.pack()
m.mainloop()


> ------------------------------------------------------------
> the problem is the window keeps adding a new time making the window ever
> increasing in size.

Because you were calling pack() in the update_stats() method, which caused it 
to pack again.  You could have forgot() the widget first, and then packed it, 
but that was unnecessary.  As you see, I packed the Entry in the __init__, so 
that it only occurs *once* when 'myclock' is created, and so doesn't pack 
repeatedly in the Frame.

Some notes:

I also create the Entry to refer to the StringVar immediately.  Then, 
whenever you update the StringVar, using set, the Entry widget automatically 
updates.

It is almost *NEVER* a good idea for a widget to pack() itself in its own 
__init__ method.  It is error prone, and makes it hard to reuse your widget.  
When you subclass Frame, you are saying that your new class *IS* a Frame, and 
will behave like a Frame (and could be used everywhere a Frame is used).  
Frames do not pack() themselves, and neither should you.  The code that 
creates myclock() should pack it (or grid it, etc.), like it would any other 
frame.  (when I started with Tkinter, I did the same thing as you, and had to 
painfully unlearn that technique)


-- 
Bay Area Python Interest Group - http://www.baypiggies.net/

Chad Netzer
cnetzer at mail.arc.nasa.gov