def str2framework(s):
    """Make sure RLlib uses a compatible framework.
    RLlib natively supports tf, tf2, and torch, but
    using lazy evaluation with tf leads to issues.
    As of now, options must be torch or tf2

    :s: Framework string

    """
    if (not s):
        return None
    s = s.lower()
    assert s in ["tf","tf2","torch"],\
        "ERROR: framework {} not supported: Please used tf, tf2, or torch"\
                                .format(s)
    return s