[Tutor] More Tkinter Help Please [callbacks and embedded functions]

[SA]

On 6/16/02 1:33 PM, "Danny Yoo" <dyoo@hkn.eecs.berkeley.edu> wrote:


> 
> I'm not too familiar with tkSimpleDialog.Dialog, so I'm not quite sure if
> there's a problem with inheritance.  Can you explain more what problems
> you're running into with this code?
> 
> 
> Ah!  I think that for this statement:
> 
>       self.b4 = Button(f, text="Save Input", command=Saving)
> 
> 
> if 'tkSimpleDialog' is the tkSimpleDialog that's in the 'Introduction To
> Tkinter' tutorial:
> 
> http://www.pythonware.com/library/tkinter/introduction/dialog-windows.htm
> 
> 
> then we need to do a little extra: the dialog box needs to know its parent
> window when it's being constructed!  Let's take a look at the definition
> of tkSimpleDialog.Dialog again:
> 
> 
> ### Sample of tkSimpleDialog.py
> # File: tkSimpleDialog.py
> 
> from Tkinter import *
> import os
> 
> class Dialog(Toplevel):
> 
>   def __init__(self, parent, title = None):
> ###
> 
> 
> So when we create a Dialog box, this dialog box must take in an additional
> 'parent' parameter.  However, back in your code:
> 
>       self.b4 = Button(f, text="Save Input", command=Saving)
> 
> When the fourth button is pressed, it tries to call the Saving dialog
> constructor with no parameters: this may be the problem that you're
> running into.  We'd like to be able to do something like:
> 
>       self.b4 = Button(f, text="Save Input", command=Saving(f))
> 
> since 'f' is the frame parent that we'd like to attach the Dialog to...
> but the problem with this is that Python will actually call Saving(f). It
> calls it too soon, because, to Python,
> 
>   Saving(f)
> 
> is a function call, so it just evaluates it straightaway.  We need a way
> to create a callback function that knows about 'f', enough so that it can
> do a 'Saving(f)' when our button is pressed.  What to do?
> 
> 
> 
> 
> 
> The solution actually isn't too bad:
> 
> ###
>       def saving_callback(): Saving(f)
>       self.b4 = Button(f, text="Save Input", command=saving_callback)
> ###
> 
> That is, we can actually embed a small function called 'saving_callback',
> and we can pass that off to as the button callback.  The miniature
> function has access to all the local variables of its parent, which is why
> saving_callback() can say 'f' without problems.
> 


Ok. Now I get a different error:

Exception in Tkinter callback
Traceback (most recent call last):
  File "/sw/src/root-python-2.2.1-6/sw/lib/python2.2/lib-tk/Tkinter.py",
line 1292, in __call__
    return apply(self.func, args)
TypeError: saving_callback() takes no arguments (1 given)


Also where does the f come from? Is it from the f = Frame(top) in  the
__init__ portion of the PyShell calss? If so, how would this carry over the
saving_callback function? Would the Dialog Box be separate from the initial
frame?

Thanks in advance.
SA