<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def getDatastreamHistory(self, pid, dsid, format=None):
        '''Get history information for a datastream.

        :param pid: object pid
        :param dsid: datastream id
        :param format: format
        :rtype: :class:`requests.models.Response`
        '''
        http_args = {}
        if format is not None:
            http_args['format'] = format
        # Fedora docs say the url should be:
        #   /objects/{pid}/datastreams/{dsid}/versions
        # In Fedora 3.4.3, that 404s but /history does not
        uri = 'objects/%(pid)s/datastreams/%(dsid)s/history' % \
            {'pid': pid, 'dsid': dsid}
        return self.get(uri, params=http_args)