[Tutor] Tkinter layout question

[Peter Otten]

Phil wrote:

> On Sun, 23 Apr 2017 09:52:16 +0200
> Peter Otten <__peter__ at web.de> wrote:
> 
>> If you wrote the above with Buttons instead of DisplayTables you'd
>> encounter the same behaviour. The problem is that you call
>> tkinter.Tk() twice (which is generally a recipe for disaster; if you
>> want multiple windows use tkinter.Toplevel() for all but the first
>> one).
>> 
>> Once you have fixed that you should be OK:
>> 
>> import tkinter as tk
>> import table_class
>> 
>> root = tk.Tk()
>> 
>> tab = table_class.DisplayTable(root,
>>                     ["Left","middle","Right"],
>>                     [[1,2,1],
>>                     [3,4,3],
>>                     [5,6,5]],
>>                     datacolor='blue',
>>                     cellcolor='yellow',
>>                     gridcolor='red',
>>                     hdcolor='black')
>> 
>> second_tab = table_class.DisplayTable(root,
>>                     ["Left","middle","Right"],
>>                     [[1,2,1],
>>                     [3,4,3],
>>                     [5,6,5]],
>>                     datacolor='blue',
>>                     cellcolor='green',
>>                     gridcolor='red',
>>                     hdcolor='black')
>> 
>> tab.pack(side=tk.LEFT)
>> second_tab.pack()
>> 
>> root.mainloop()
> 
> Thank you again Peter. Of course your changes worked but at the moment I'm
> not sure why.
> 
> if root = tk.Tk() then why isn't table_class.DisplayTable(root, the same
> as table_class.DisplayTable(tk.Tk(),. Obviously it isn't but I don't know
> why.

Consider the function make_a_cake(). If you use it

eat_a_piece_of(make_a_cake())
eat_a_piece_of(make_a_cake())

that's short for

one_cake = make_a_cake()
eat_a_piece_of(one_cake)

another_cake = make_a_cake()
eat_a_piece_of(another_cake)

i. e. you had two pieces of cake, one piece of each of two cakes.

If you write

cake = make_a_cake()
eat_a_piece_of(cake)
eat_a_piece_of(cake)

you have still eaten two pieces of cake but both are taken from the same 
cake.

Likewise when you write

root = tk.Tk()
first_table = DisplayTable(root)
second_table = DisplayTable(root)

both tables share the same instance of the Tk class.
 
> Also I found that root.mainloop() isn't necessary in that the result is
> the same with or without. Perhaps it serves some other purpose?

Try running it from the command line, not in idle. In every tkinter program 
there must be a main loop to respond to events.