code: def prepare(self, start=-1):
          
          if start == -1:
              start = self.grammar.start
          self.root = None
          current_node = Node(start, None, [], 0, 0)
          self.stack = []
          self.stack.append((self.grammar.dfas[start - 256], 0, current_node))
docs: Setup the parser for parsing.
  
          Takes the starting symbol as an argument.