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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 max(self, key=None):
 """ Get the max value of a given key. :param key: The key :type key: str or None :rtype: mixed """


        def _max(result, item):
            val = data_get(item, key)

            if result is None or val > result:
                return value

            return result

        return self.reduce(_max)