Delegated property pattern

# See http://stackoverflow.com/questions/14167675 for more

def _make_credentials_property(name):
  def get(self):
    return getattr(self.credentials, name)
  def set(self, value):
    setattr(self.credentials, name, value)
  return property(get, set)


class OAuth2TokenFromCredentials(object):
  def __init__(self, credentials):
    self.credentials = credentials
  access_token = _make_credentials_property('access_token')
  ...
  _invalid = _make_credentials_property('invalid')