Push to Make (Single Pole) Button running a loop

[Jon Todd]

Happy holidays all!

I'm developing an application and, as a relative newbie to Python, have come 
across a stumbling block with Tkinter.

I'd like to have a button that when pressed executes a loop (this could be a 
thread) and then stops execution when it's released (Push to Make - Single 
Pole in electronics terms).

I've tried the regular way of associating the procedure with a callback and 
tried using <Button-1> and <ButtonRelease-1> bindings but am getting nowhere 
fast (in the latter case the button release event seems to occur anyhows).

So my question is: Is there a neat way of doing this? And would it 
necessarily involve creating a custom widget?

...

Also, while I'm here, what's the state of play regarding non-ASCII in 
Tkinter widgets. I've been trying to get our currency symbol, £, to display 
but didn't have much luck even playing with the coding: settings.

TIA

jon