kivy/kivy — pull request #1432 by Ian-Foote (2013-08-10 15:53:16+00:00)
Title: Use widget's id as its __hash__.

Using `id` for a widget's `__hash__` is safe because `__eq__` only returns `True` if it is the same object. Fixes a `TypeError` in `ButtonBehaviour` `on_touch` methods in python3.