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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 account_data(self, address, key):
 """This endpoint represents a single data associated with a given account. `GET /accounts/{account}/data/{key} <https://www.stellar.org/developers/horizon/reference/endpoints/data-for-account.html>`_ :param str address: The account ID to look up a data item from. :param str key: The name of the key for the data item in question. :return: The value of the data field for the given account and data key. :rtype: dict """

        endpoint = '/accounts/{account_id}/data/{data_key}'.format(
            account_id=address, data_key=key)
        return self.query(endpoint)