How to use the numerapi.utils.parse_datetime_string function in numerapi

def test_parse_datetime_string():
    s = "2017-12-24T20:48:25.90349Z"
    t = datetime.datetime(2017, 12, 24, 20, 48, 25, 903490, tzinfo=tzutc())
    assert utils.parse_datetime_string(s) == t
    assert utils.parse_datetime_string(None) is None

def test_parse_datetime_string():
    s = "2017-12-24T20:48:25.90349Z"
    t = datetime.datetime(2017, 12, 24, 20, 48, 25, 903490, tzinfo=tzutc())
    assert utils.parse_datetime_string(s) == t
    assert utils.parse_datetime_string(None) is None

mutation($value: String!
                   $type: String!) {
              v2ChangeStake(value: $value
                            type: $type) {
                dueDate
                requestedAmount
                status
                type
              }
        }
        '''
        arguments = {'value': str(nmr), 'type': action}
        result = self.raw_query(query, arguments, authorization=True)
        stake = result['data']['v2ChangeStake']
        utils.replace(stake, "requestedAmount", utils.parse_float_string)
        utils.replace(stake, "dueDate", utils.parse_datetime_string)
        return stake

openTime
                  resolveTime
                  resolvedGeneral
                  resolvedStaking
                }
              }
            }
          }
        """
        data = self.raw_query(query, authorization=True)['data']
        payments = data['user']
        # convert strings to python objects
        for p in payments['payments']:
            utils.replace(p['round'], "openTime", utils.parse_datetime_string)
            utils.replace(p['round'], "resolveTime",
                          utils.parse_datetime_string)
            utils.replace(p, "usdAmount", utils.parse_float_string)
            utils.replace(p, "nmrAmount", utils.parse_float_string)
        for p in payments['reputationPayments']:
            utils.replace(p, "nmrAmount", utils.parse_float_string)
            utils.replace(p, "insertedAt", utils.parse_datetime_string)
        for p in payments['otherUsdIssuances']:
            utils.replace(p, "usdAmount", utils.parse_float_string)
            utils.replace(p, "insertedAt", utils.parse_datetime_string)
        return payments

False
        """
        query = '''
            query($tournament: Int!) {
              rounds(tournament: $tournament
                     number: 0) {
                number
                openTime
              }
            }
        '''
        arguments = {'tournament': tournament}
        raw = self.raw_query(query, arguments)['data']['rounds'][0]
        if raw is None:
            return False
        open_time = utils.parse_datetime_string(raw['openTime'])
        now = datetime.datetime.utcnow().replace(tzinfo=pytz.utc)
        is_new_round = open_time > now - datetime.timedelta(hours=hours)
        return is_new_round