I have noticed an issue with using the tag add command of a ttk.Treeview widget when activated with the tk.call() method. That is, it can't handle white space in the value of the str() elements of its items argument.

See this answer on how I had implemented the tag add command. Now if /home/user/Desktop/Secret Source is passed in to items, the returned error msg is:

self.tk.call(self.tree._w, 'tag', 'add', tag, items)
_tkinter.TclError: Item /home/user/Desktop/Secret not found

The text Source with one white space is missing from Secret Source. How do I overcome this error?

The treeview tag add command requires items to be a list, but you're passing a string. When tcl is given a string when it expects a list, the string will be split on whitespace to create a list. That is why it thinks the characters before the space is the whole item id.