Instanciate a singleton per scope.

def singleton_per_scope(_cls, _scope=None, _renew=False, *args, **kwargs):
    """Instanciate a singleton per scope."""

    result = None

    singletons = SINGLETONS_PER_SCOPES.setdefault(_scope, {})

    if _renew or _cls not in singletons:
        singletons[_cls] = _cls(*args, **kwargs)

    result = singletons[_cls]

    return result