def __init__(self, widget, tks, tk_event):
self._widget = widget<EOL>self._tks = tks<EOL>self._tk_event = tk_event<EOL>self._callbacks = {}<EOL>self._func_ids = []<EOL>for tk in self._tks:<EOL><INDENT>func_id = tk.bind(tk_event, self._event_callback)<EOL>self._func_ids.append(func_id)<EOL><DEDENT>
The EventCallback handles all the callbacks for a single tk event
(e.g. <Button-1>) on a guizero widget.

By using the EventCallback structure you can assign multiple callbacks
to 1 tk event across multiple tk widgets.