A Configurator

configurator.py

class Configurator:
    def __init__(self, defaults, parent=None):
        self.store = {}
        self.parent = parent

        for k, v in defaults.items():
            self.store[k] = (None, v)


    def get(self, key):
        try:
            setting, default = self.store[key]
        except KeyError:
            if self.parent:
                return self.parent.get(key)

        if setting:
            return setting
        return self.parent.get(key) if self.parent else None


    def __getitem__(self, key):
        def find(self, key):
            try:
                setting, default = self.store[key]
            except KeyError:
                if self.parent:
                    return find(self.parent, key)
                else:
                    raise
            return setting if setting else default

        value = self.get(key)
        return value if value else find(self, key)


    def __setitem__(self, key, value):
        try:
            _, default = self.store[key]
        except KeyError:
            default = None

        self.store[key] = (value, default)


if __name__ == "__main__":
    parent = Configurator({
        "foo": "foobar",
        "baz": "something else"
    })

    store = Configurator({ "foo": "replaced foobar" }, parent=parent)

    print(store["foo"])
    print(store["baz"])

    parent["foo"] = "setting foo parent!"
    parent["baz"] = "setting baz parent!"

    print(store["foo"])
    print(store["baz"])

    store["baz"] = "setting baz store!"

    print(store["foo"])
    print(store["baz"])