'Path Distance Similarity:
Return a score denoting how similar two word senses are, based on the
shortest path that connects the senses in the is-a (hypernym/hypnoym)
taxonomy. The score is in the range 0 to 1, except in those cases where
a path cannot be found (will only be true for verbs as there are many
distinct verb taxonomies), in which case None is returned. A score of
1 represents identity i.e. comparing a sense with itself will return 1.
:type other: Synset
:param other: The ``Synset`` that this ``Synset`` is being compared to.
:type simulate_root: bool
:param simulate_root: The various verb taxonomies do not
share a single root which disallows this metric from working for
synsets that are not connected. This flag (True by default)
creates a fake root that connects all the taxonomies. Set it
to false to disable this behavior. For the noun taxonomy,
there is usually a default root except for WordNet version 1.6.
If you are using wordnet 1.6, a fake root will be added for nouns
as well.
:return: A score denoting the similarity of the two ``Synset`` objects,
normally between 0 and 1. None is returned if no connecting path
could be found. 1 is returned if a ``Synset`` is compared with
itself.'

def path_similarity(self, other, verbose=False, simulate_root=True):

    distance = self.shortest_path_distance(other, simulate_root=(simulate_root and self._needs_root()))
    if ((distance is None) or (distance < 0)):
        return None
    return (1.0 / (distance + 1))
