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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 at(self, root):
 """Set root where PyJsonq start to prepare :@param root :@type root: string :@return self :@throws KeyError """

        leafs = root.strip(" ").split('.')
        for leaf in leafs:
            if leaf:
                self._json_data = self.__get_value_from_data(leaf, self._json_data)
        return self