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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 getAttribute(self, attr: str) -> _AttrValueType: """Get attribute of this node as string format. If this node does not have ``attr``, return None. """

        if attr == 'class':
            if self.classList:
                return self.classList.toString()
            return None
        attr_node = self.getAttributeNode(attr)
        if attr_node is None:
            return None
        return attr_node.value