Example of simple callback / lambda function default thing in python2.

gistfile1.py

from __future__ import print_function

class AccessControl:
	def __init__(self, **kwargs):
		self.on_grant = kwargs.get('on_grant', lambda: print(1) )

	def grant(self):
		self.on_grant()


a = AccessControl(on_grant = lambda: print(2))
a.on_grant = lambda: print(3)
a.grant()