def __init__(self, l, containerType):
        """
        @param l: The list of object which may contain some not yet referenced
        objects.

        @param containerType: A type of container objects (e.g., C{tuple} or
            C{set}).
        """
        NotKnown.__init__(self)
        self.containerType = containerType
        self.l = l
        self.locs = list(range(len(l)))
        for idx in range(len(l)):
            if not isinstance(l[idx], NotKnown):
                self.locs.remove(idx)
            else:
                l[idx].addDependant(self, idx)
        if not self.locs:
            self.resolveDependants(self.containerType(self.l))

        @param l: The list of object which may contain some not yet referenced
        objects.

        @param containerType: A type of container objects (e.g., C{tuple} or
            C{set}).
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/persisted/crefutil.py