def _get_key_from_raw_synset(raw_synset):
    """Derives synset key in the form of `lemma.pos.sense_no` from the provided eurown.py Synset class,

    Notes
    -----
    Internal function. Do not call directly.


    Parameters
    ----------
    raw_synset : eurown.Synset
      Synset representation from which lemma, part-of-speech and sense is derived.

    Returns
    -------
    string
      Key of the synset in the form of `lemma.pos.sense_no`.
      
    """
    pos = raw_synset.pos
    literal = raw_synset.variants[0].literal
    sense = '%02d' % raw_synset.variants[0].sense
    return '.'.join([literal, pos, sense])
