def export(self, query, **params):
        """Runs a search and immediately starts streaming preview events.
        This method returns a streaming handle to this job's events as an XML
        document from the server. To parse this stream into usable Python objects,
        pass the handle to :class:`splunklib.results.ResultsReader`::

            import splunklib.client as client
            import splunklib.results as results
            service = client.connect(...)
            rr = results.ResultsReader(service.jobs.export("search * | head 5"))
            for result in rr:
                if isinstance(result, results.Message):
                    # Diagnostic messages may be returned in the results
                    print '%s: %s' % (result.type, result.message)
                elif isinstance(result, dict):
                    # Normal events are returned as dicts
                    print result
            assert rr.is_preview == False

        Running an export search is more efficient as it streams the results
        directly to you, rather than having to write them out to disk and make
        them available later. As soon as results are ready, you will receive
        them.

        The ``export`` method makes a single roundtrip to the server (as opposed
        to two for :meth:`create` followed by :meth:`preview`), plus at most two
        more if the ``autologin`` field of :func:`connect` is set to ``True``.

        :raises `ValueError`: Raised for invalid queries.
        :param query: The search query.
        :type query: ``string``
        :param params: Additional arguments (optional). For a list of valid
            parameters, see `GET search/jobs/export
            <http://docs/Documentation/Splunk/latest/RESTAPI/RESTsearch#search.2Fjobs.2Fexport>`_
            in the REST API documentation.
        :type params: ``dict``

        :return: The ``InputStream`` IO handle to raw XML returned from the server.
        """
        if "exec_mode" in params:
            raise TypeError("Cannot specify an exec_mode to export.")
        params['segmentation'] = params.get('segmentation', 'none')
        return self.post(path_segment="export",
                         search=query,
                         **params).body