changeproy.py

# written in browser#

class ChangeProxy(object):
  def __init__(self, observed, tracker):
    self.__observed = observed
    self.__tracker = tracker
    
  def __getattr__(self, key):
    if key in self.__tracker:
      return self.__tracker[key]
    return getattr(self.__observed, key)
    
  def __setattr__(self, key, value):
    self.__tracker[key] = value
    
@contextmanager
def update(observed):
  updates = {}
  proxy = ChangeProxy(observed, updates
  try:
    yield proxy
  except:
    pass
  else:
    observed.update(updates)