[Tutor] binding problem

[Peter Otten]

Chris Hare wrote:

> Thanks for the advice.  When I do that, I get this error
> 
> Exception in Tkinter callback
> Traceback (most recent call last):
>   File
>   
"/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/lib-
tk/Tkinter.py",
>   line 1410, in __call__
>     return self.func(*args)
> TypeError: focus_set() takes exactly 1 argument (2 given)
> 
> In situations like this where the function isn't one you wrote, how to you
> debug these?

In this case there is not much to debug, the error message says it all: you 
have an extra argument that the focus_set() method doesn't accept. The 
simplest way to drop that argument is to wrap the method call:

def focus_set(event): # only one arg because it's a function, not a method
    self.login_userid.focus_set()

self.list.bind("<Button-1>", focus_set)

This is sometimes written with a lambda function

self.list.bind("<Button-1>", lambda event: self.login_userid.focus_set())

If you wanted to learn more about that extra argument you could temporarily 
replace the callback with something that can give you the necessary 
information, e. g.

def inspect_args(*args):
    for arg in args:
         print arg
         print vars(arg)

self.list.bind("<Button-1>", inspect_args)

As a last resort and an idea almost too revolutionary to mention in public, 
you could read some tutorial or documentation...