<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def make_query(self, query_type, expression, **kwargs):
 """ Actually perform the query, try to convert datetime to isoformat on the fly """

        data = dict(expression=str(expression),
                    stop=kwargs.get('stop', datetime.utcnow()))
        data.update(kwargs)

        for k in ['start', 'stop']:
            if k in data:
                try:
                    data[k] = data[k].isoformat()
                except AttributeError:
                    pass

        r = requests.get(self.evaluator_url + query_type, params=data)
        r.raise_for_status()

        return r.json()