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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 _reset(self):
 """ Rebuilds structure for AST and resets internal data. """


        self._filename = None
        self._block_map = {}
        self._ast = []
        self._ast.append(None)  # header
        self._ast.append([])    # options list
        self._ast.append([])