Django snippets

class DiffingMixin(object):
	def __init__(self, *args, **kwargs):
		  super(DiffingMixin, self).__init__(*args, **kwargs)
		  self._original_state = dict(self.__dict__)
	def save(self, *args, **kwargs):
		state = dict(self.__dict__)
		del state['_original_state']
		self._original_state = state
		super(DiffingMixin, self).save()
	def is_dirty(self):
		missing = object()
		result = {}
		for key, value in self._original_state.iteritems():
		  if value != self.__dict__.get(key, missing):
				return True
		return False
	def changed_columns(self):
		missing = object()
		result = {}
		for key, value in self._original_state.iteritems():
		  if value != self.__dict__.get(key, missing):
				result[key] = {'old':value, 'new':self.__dict__.get(key, missing)}
		return result