def getattr(self, key, default=None, callback=None):
        u"""Getting the attribute of an element.

        >>> xml = etree.Element('root')
        >>> xml.text = 'text'
        >>> Node(xml).getattr('text')
        'text'
        >>> Node(xml).getattr('text', callback=str.upper)
        'TEXT'
        >>> Node(xml).getattr('wrong_attr', default='default')
        'default'
        """
        value = self._xml.text if key == 'text' else self._xml.get(key, default)
        return callback(value) if callback else value