Tk.split() doesn't work with nested Unicode strings, but works with nested bytes.

>>> import tkinter
>>> t = tkinter.Tcl()
>>> t.split('a {b c}')
('a', ('b', 'c'))
>>> t.split(b'a {b c}')
('a', ('b', 'c'))
>>> t.split(('a {b c}',))
('a {b c}',)
>>> t.split((b'a {b c}',))
(('a', ('b', 'c')),)

I think this is unintentional. Here is a patch which processes strings inside a tuple as bytes objects. It also adds tests for Tk.splitline() and Tk.split().