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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def prepare(self, start=-1):
 """Setup the parser for parsing. Takes the starting symbol as an argument. """

        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))