code: def notify_observers(self, which=None, min_priority=None):
          
          if self._update_on:
              if which is None:
                  which = self
              if min_priority is None:
                  [callble(self, which=which) for _, _, callble in self.observers]
              else:
                  for p, _, callble in self.observers:
                      if p <= min_priority:
                          break
                      callble(self, which=which)
docs: Notifies all observers. Which is the element, which kicked off this
          notification loop. The first argument will be self, the second `which`.
  
          .. note::
             
             notifies only observers with priority p > min_priority!
             
          :param min_priority: only notify observers with priority > min_priority
                               if min_priority is None, notify all observers in order