kivy/kivy — pull request #2724 by kived (2014-12-04 23:43:56+00:00)
Title: assert that event callbacks are actually callable

To avoid having to dig through code and guess at where the bad callback is bound.

````
Traceback (most recent call last):
File "evttest.py", line 21, in
TestApp().run()
File "/home/ryan/git/aeris2/kivy/kivy/app.py", line 799, in run
root = self.build()
File "evttest.py", line 17, in build
root.bind(text=True)
File "kivy/_event.pyx", line 398, in kivy._event.EventDispatcher.bind (kivy/_event.c:4947)
assert callable(value), '{!r} is not callable'.format(value)
AssertionError: True is not callable
````