[Kivy] Not listen for multi clicks

[Barrowman]

change

def increase(self):
self.nr += 1
sleep(1) # Do some heavy stuff
self.ids.nr_label.text = str(self.nr)

to

 if self.nr == 0:
        self.nr = 1
        self.ids.nr_label.text = str(self.nr)
    else: return()

You seem to be thinking that the sleep will allow something else to be going on but it won't.