def step(self, dt):
		already_run = set()
		for key in self.held_keys:
			func = self._key_hold_map.get(key)
			if func is not None and func not in already_run:
				already_run.add(func)
				func(dt)
invoke held key functions
dataset/ETHPy150Open caseman/grease/grease/controls.py/KeyControls.step