> I don't see in what way it would break existing applications. The
> indices returned by that command in Tcl should all be represented as
> strings in Python, so I see this at max causing a double attempt to
> convert it to str.

I can't quite follow your terminology: what indices?

I can imagine many cases where conversion using Python's str() gives
a different result than the conversion through Tcl objects. For example,
if Python returns a bool, 2.5 will pass 'True' to Tcl. 2.6 will convert
this to a Tcl boolean, whose string representation is '1'.

If you are saying that the Python command *should* return strings
always, then this assumption is precisely a candidate for breakage:
people might currently be returning all kinds of things to Tcl in
callbacks (even outside Tkinter), and we might break these
applications.