The only documentation on “createfilehandle” and friends that I can find looks like it needs updating:

https://docs.python.org/release/3.4.0/faq/gui.html#can-i-have-tk-events-handled-while-waiting-for-i-o

I have been using the equivalent of this instead, for both Python 2 and 3:

import tkinter
widget = tkinter.Tk()
widget.tk.createfilehandler(file, tkinter.READABLE | tkinter.WRITABLE, callback)
...
widget.tk.deletefilehandler(file)

However I have no idea if this is a supported, proper way, if one even still exists. The old way was removed by Issue 3638.

BTW, there is a link to release/3.4.1 documentation but that returned a 404 error for me, so I linked to the 3.4.0 doc instead.