检测光标是否在文本小部件中

I am writing a text editor in Python 3 with tkinter, and I'm trying to add an undo function, but in order to log the user's edits I need to log the edit when they type a letter. However, I don't want to log the typed letter if they have clicked out of the text widget. My question is this:I am writing a text editor in Python 3 with tki