Returns a signature size for the input
    :param msg:
    :return:

def get_signature_size(msg):
    """
    Returns a signature size for the input
    :param msg:
    :return:
    """
    if isinstance(msg, (TxinGen, TxinToScript, TxinToScriptHash)):
        return 0
    elif isinstance(msg, TxinToKey):
        return len(msg.key_offsets)
    else:
        raise ValueError('Unknown tx in')