Class and tkinter problem

[Paulo da Silva]

Às 20:35 de 07/01/21, Terry Reedy escreveu:
> On 1/7/2021 4:20 AM, Terry Reedy wrote:
>> On 1/7/2021 2:42 AM, Christian Gollwitzer wrote:
>>> Am 07.01.21 um 08:29 schrieb Paulo da Silva:
>>>
>>>> Does anybody know why cmd method isn't called when I change the button
>>>> state (clicking on it) in this example?
>>>> I know that this seems a weird class use. But why doesn't it work?
>>>> Thanks.
>>>>
>>>> class C:
>>>>      from tkinter import Checkbutton
>>>>      import tkinter
>>>>
>>>>      @staticmethod
>>> ^^it works if you remove the staticmethod here
>>
>> staticmethods are essentially useless in Python.  What little was
>> gained by their addition is partly offset by the introduced confusion.
> 
>>>>      def cmd():
>>>>          print("Test")
> 
> The confusion is that methods are callable, whereas 'staticmethods' are
> not.  I was not completely aware of this until pointed out by Peter
> Otten with example
> 
> "    cmd()
> 
> Traceback (most recent call last):
>   File "<pyshell#28>", line 1, in <module>
>     class C:
>   File "<pyshell#28>", line 4, in C
>     cmd()
> TypeError: 'staticmethod' object is not callable
> 
> You have to go through the descriptor protocol:"
> 
> Indeed, dir(cmd) shows that it does not have a .__call__ attribute.
> 
>>      top=tkinter.Tk()
>>      cb=Checkbutton(command=cmd)
> 
>> Button commands have to be tcl functions.  Tkinter wraps Python
>> functions as tcl function.  Static methods also wrap python functions,
>> as a .__func__ attribute.  So the code if one passes cmd.__func__.
> 
> "So the code works if one passes the callable cmd.__func__."
> 
>>> Maybe there is a bug in tkinter, that it doesn't work with static
>>> methods?
>>
>> One could propose that tkinter test whether callables are staticmethods 
> 
> Command options, as documented, must be callables. Neither staticmethods
> nor classmethods are callable.
> 
>> and unwrap them when they are.
> 
>  I would propose instead that if possible tkinter raise TypeError when
> passed a non-callable as a command.
> 
Yes, that would be much better.
Thanks.