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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 evaluate(self, node, filename=None):
 """ Evaluate a source string or node, using ``filename`` when displaying errors. """

        if isinstance(node, string_types):
            self.source = node
            kwargs = {'mode': 'eval'}
            if filename:
                kwargs['filename'] = filename
            try:
                node = ast.parse(node, **kwargs)
            except SyntaxError as e:
                s = self.get_fragment(e.offset)
                raise SyntaxError('syntax error %s' % s)
        node_type = node.__class__.__name__.lower()
        handler = self.get_handler(node_type)
        if handler is None:
            if self.source is None:
                s = '(source not available)'
            else:
                s = self.get_fragment(node.col_offset)
            raise SyntaxError("don't know how to evaluate %r %s" % (
                node_type, s))
        return handler(node)