def lookup():
    """Attempt to resolve an entry in the cache.

        The instance is instructed to look for the cache key that it was
        informed about via the call to ``setcachekey()``.

        If there's no cache hit or the cacher doesn't wish to use the cached
        entry, ``None`` should be returned.

        Else, a dict defining the cached result should be returned. The
        dict may have the following keys:

        objs
           An iterable of objects that should be sent to the client. That
           iterable of objects is expected to be what the command function
           would return if invoked or an equivalent representation thereof.
        """
