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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 get_tx(tx_id, api_code=None):
 """Get a single transaction based on a transaction hash. :param str tx_id: transaction hash to look up :param str api_code: Blockchain.info API code (optional) :return: an instance of :class:`Transaction` class """


    resource = 'rawtx/' + tx_id
    if api_code is not None:
        resource += '?api_code=' + api_code
    response = util.call_api(resource)
    json_response = json.loads(response)
    return Transaction(json_response)