How to use the punq.__init__.ResolutionTarget function in punq

def __init__(self, key, impls):
        self.targets = {key: ResolutionTarget(key, impls)}
        self.cache = {}
        self.service = key

def build_context(self, key, existing=None):
        if existing is None:
            return ResolutionContext(key, list(self.__getitem__(key)))

        if key not in existing.targets:
            existing.targets[key] = ResolutionTarget(key, list(self.__getitem__(key)))

        return existing