Actually perform the query,
        try to convert datetime to isoformat on the fly

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()