Limiting entry on a tk widget

Question

I have trouble finding a way to limit the entry length of entry widgets, I would like to limit it to 20 characters, i.e. when I click on a sequence or the other I would like

Answer 1

The simplest solution is to put a trace on the variable. When the trace fires, check the length of the value and then delete any characters that exceed the limit.

If you don't like that solution, Tkinter also has built-in facilities to do input validation on entry widgets. This is a somewhat under-documented feature of Tkinter. For an example, see my answer to the question Python/Tkinter: Interactively validating Entry widget content