I wrote a very simple SMILES parser using pyparsing https://github.com/dakoner/smilesparser/tree/master I wouldn't say it's intended for production work, but it has been useful in situations where I didn't want to pull in rdkit.

I see you include the dot disconnect "." as part of the Bond definition.

You also define Chain as:

  Chain <<= pp.Group(pp.Optional(Bond) + pp.Or([Atom, RingClosure]))