code: def string_to_transition(s):
      
      from .machines import Transition
      s = lexer(s)
      lhs = parse_multiple(s, parse_store)
      if s.pos < len(s) and s.cur == "->":
          s.pos += 1
          rhs = parse_multiple(s, parse_store)
      else:
          rhs = ()
      parse_end(s)
      return Transition(lhs, rhs)
docs: s is a string of the form a,b or a,b->c,d