How to obtain trigger callback returns

[frthjf]

First, thanks for this neat package! It looks like it's not possible to obtain the return value of the triggered callbacks as trigger('foo') always returns True.

However, I think it would be nice to have this option to use callbacks to influence the control flow. Consider the following example where an event is triggered in a save method.

def save(data):
      observable.trigger('save', data)
      with open('bla.txt') as f: 
           f.write(data)
# ...

observable.on('save', lambda data: True)

The user can hook into the save method but the callback cannot send anything back to influence what's happening at the trigger point, like here:

def save(data):
      if observable.trigger('save', data) is False:
          return
      with open('bla.txt') as f: 
           f.write(data)
# ...

def custom_save(data):
      with open('a_differnt_save_method.txt') as f:
            f.write(data)
      return False   # returns False to prevent execution of default save logic

observable.on('save', custom_save)

If trigger would collect the callback returns such 'extension via event' could be implemented. Would you consider enhancing the trigger behaviour?

[frthjf]

Looking a bit more closely, if I change the trigger function to

    def trigger(self, event: str, *args: T.Any, **kw: T.Any) -> list:
        callbacks = list(self._events.get(event, []))
        return [callback(*args, **kw) for callback in callbacks]

the return is not bool any longer. However, it would behave like it since bool([]) is False. I'd be happy to prepare a pull request for that.