PyCS/pycs/observable/Observable.py

class Observable:
    @staticmethod
    def create(source, parent=None, key=None):
        from . import ObservableDict
        from . import ObservableList

        if isinstance(source, ObservableDict) or isinstance(source, ObservableList):
            source.parent = parent
            source.key = key
            return source
        if isinstance(source, dict):
            return ObservableDict(source, parent, key)
        if isinstance(source, list):
            return ObservableList(source, parent, key)
        else:
            return source

    def __init__(self, parent, key):
        self.parent = parent
        self.key = key
        self.subscriptions = []

    def subscribe(self, handler, immediate=False):
        self.subscriptions.append(handler)

        if immediate:
            handler(self, [])

    def notify(self, keys=None):
        if keys is None:
            keys = []

        for s in self.subscriptions:
            s(self, keys)

        if self.parent is not None:
            if self.key is None:
                raise ValueError

            keys.insert(0, self.key)
            self.parent.notify(keys)