def _merge_lib_dict(d1, d2):
    """ Merges lib_dict `d2` into lib_dict `d1`
    """
    for required, requirings in d2.items():
        if required in d1:
            d1[required].update(requirings)
        else:
            d1[required] = requirings
    return None
Merges lib_dict `d2` into lib_dict `d1`