once.py

def stable (value):
	return lambda *args, **kwargs: value

def once_per_object (unstable):
	"""Method decorator. Run only once 'unstable' per instance"""
	def stabilize (*args, **kwargs):
		self = args [0]
		result = unstable (*args, **kwargs)
		setattr (self, unstable.__name__, stable (result))
		return result
	return stabilize

def once (unstable):
	"""Method decorator. Run only once 'unstable'."""
	def stabilize (*args, **kwargs):
		self = args [0]
		result = unstable (*args, **kwargs)
		setattr (self.__class__, unstable.__name__, stable (result))
		return result
	return stabilize