Key Binding Problem

[Terry Reedy]

On 3/23/2016 12:28 AM, Wildman via Python-list wrote:
> On Wed, 23 Mar 2016 03:02:51 +0000, MRAB wrote:
>
>> On 2016-03-23 02:46, Wildman via Python-list wrote:
>>> My question is how do I coax bind into executing the
>>> button procedures?  Or is there a way to generate the
>>> button click event from the binding?
>>>
>> It won't let you bind to a function called "load_image" because there
>> isn't a function called "load_image"!
>>
>> The "Window" class, however, does have a method with that name.
>>
>> Try binding the keys in Window.__init__ or Window.init_window:
>>
>>       def init_window(self):
>>           ...
>>           root.bind("<l>", self.load_image)
>
> Here is what I tried:
>
> class Window(tk.Frame):
>
>      def __init__(self, master = None):
>          tk.Frame.__init__(self,master)
>          self.master = master
>          root.bind("l", self.load_image)
>
> I get this error and it doesn't make any sense to me:
>
> Exception in Tkinter callback
> Traceback (most recent call last):
>    File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 1535, in __call__
>      return self.func(*args)
> TypeError: load_image() takes exactly 1 argument (2 given)

Event handlers must have one parameter (other than 'self' for methods), 
the event, as that is what they will be passed.  You defined load_image 
like this.

     def load_image(self):
         # load image file

It should be this

     def load_image(self, event):
         # load image file

You are free to ignore the event object and some people then name the 
parameter '_' (or dummy) to signify that it will be ignored.

     def load_image(self, _):
         # load image file

You must pass the bound method, as you did, and not the function itself 
(which has two parameters).

-- 
Terry Jan Reedy