> If the issue really boils down to incorrectly passing a single string when there is only one item in 'values', and a single-item tuple should be used instead, then shouldn't the better solution be for Python to handle this automatically and re-cast the errant string into a tuple?

Tkinter is rather a thin wrapper around Tcl/Tk. I just passes values to Tcl. Tcl is a weak typed language. Internally it can use different types for performance, but semantically all are strings. "a b" is a string and a 2-element list, and a 1-element dict at the same time. It is Tcl try to re-cast the errant string into a Tcl list, and fails because it has incorrect syntax. Python can't know your intention. It supposes that you know what you do. If under re-casting you meant passing a string to a tuple constructor, `tuple(values)`, this will be obviously wrong. If your meant parsing a string to a tuple at Python side -- it will file as well as parsing it at Tcl side. If you meant wrapping a string into a one-element tuple, `(values,)`, this can break working code when a user intentionally passes a space separated list of words:

    tv.insert("", END, values=(foo, bar), tags="foo bar")

Additionally, any special cases will complicate the code of Tkinter (currently it is rather a thin wrapper) and complicate the mental model.