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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 send_batch(messages, api_key=None, secure=None, test=None, **request_args):
    '''Send a batch of messages.

    :param messages: Messages to send.
    :type message: A list of `dict` or :class:`Message`
    :param api_key: Your Postmark API key. Required, if `test` is not `True`.
    :param secure: Use the https scheme for the Postmark API.
        Defaults to `True`
    :param test: Use the Postmark Test API. Defaults to `False`.
    :param \*\*request_args: Keyword arguments to pass to
        :func:`requests.request`.
    :rtype: :class:`BatchSendResponse`
    '''
    return _default_pyst_batch_sender.send(messages=messages, api_key=api_key,
                                           secure=secure, test=test,
                                           **request_args)