How to use the whisper.fetch function in whisper

# debug
        print "sending message"
        print '-' * 70
        print message

        # send!
        sock.sendall(message)
        time.sleep(2) # NB - allows file operations to complete

        # check if data file was created

        tagFile = os.path.join(temp_dir, "storage","whisper","folder", tag + ".wsp")
        self.assertTrue(os.path.exists(tagFile))

        print(whisper.fetch(tagFile, now - self.step*(num_data_points), now))

        data_period_info, stored_data = whisper.fetch(tagFile, now - self.step*(num_data_points), now)

        for whisper_data, sent_data in zip(reversed(stored_data), reversed(data)):
            self.assertAlmostEquals(whisper_data, sent_data[1])

time.sleep(stime)


            aggregated_data = aggregate(to_aggregate)
            data.append(  aggregated_data  )
            print(aggregated_data)
            print('')

        print('')

        time.sleep(2) # NB - allows file operations to complete

        tagFile = os.path.join(temp_dir, "storage","whisper","folder", tag + ".wsp")

        self.assertTrue(os.path.exists(tagFile))
        data_period_info, stored_data = whisper.fetch(tagFile, start-1, time.time())
        print('Whisper data period : ' + str(data_period_info))
        print('Whisper data : ' + str(stored_data))
        print('Data expected: ' + str(data))
        print len(stored_data)
        print(zip(stored_data, data))
        for whisper_data, sent_data in zip(stored_data, data)[:-1]:     # :D
            self.assertAlmostEquals(whisper_data, sent_data)

archive_step = 1
        whisper.create(wsp, [(archive_step, archive_len)])

        # given too many points than the db can hold
        excess_len = 1
        num_input_points = archive_len + excess_len
        test_now = int(time.time())
        input_start = test_now - num_input_points + archive_step
        input_points = [(input_start + i, random.random() * 10)
                        for i in range(num_input_points)]

        # when the db is updated with too many points
        whisper.update_many(wsp, input_points, now=test_now)

        # then only the most recent input points (those at the end) were written
        actual_time_info = whisper.fetch(wsp, 0, now=test_now)[0]
        self.assertEqual(actual_time_info,
                         (input_points[-archive_len][0],
                          input_points[-1][0] + archive_step,  # untilInterval = newest + step
                          archive_step))

def test_heal_target_missing(self):
        testdb = "test-%s" % self.db
        try:
            os.unlink(testdb)
        except (IOError, OSError):
            pass

        self._removedb()

        schema = [(1, 20)]
        self._createdb(self.db, schema)
        original_data = whisper.fetch(self.db, 0)

        # This should log complaints but exit successfully as it cannot
        # heal its target /dev/null
        heal_metric(self.db, testdb)
        data = whisper.fetch(testdb, 0)
        self.assertEqual(original_data, data)

def test_update_single_archive(self):
        """
        Update with a single leveled archive
        """
        retention_schema = [(1, 20)]
        data = self._update(schema=retention_schema)
        # fetch the data
        fetch = whisper.fetch(self.filename, 0)   # all data
        fetch_data = fetch[1]

        for i, (timestamp, value) in enumerate(data):
            # is value in the fetched data?
            self.assertEqual(value, fetch_data[i])

        # check TimestampNotCovered
        with AssertRaisesException(
                whisper.TimestampNotCovered(
                    'Timestamp not covered by any archives in this database.')):
            # in the futur
            whisper.update(self.filename, 1.337, time.time() + 1)

        with AssertRaisesException(
                whisper.TimestampNotCovered(
                    'Timestamp not covered by any archives in this database.')):

def test_heal_source_corrupt(self):
        testdb = "/dev/null"
        self._removedb()

        schema = [(1, 20)]
        self._createdb(self.db, schema)
        original_data = whisper.fetch(self.db, 0)

        # This should log complaints but exit successfully as it cannot
        # read from the source /dev/null
        heal_metric(testdb, self.db)
        data = whisper.fetch(self.db, 0)
        self.assertEqual(original_data, data)

pass

        schema = [(1, 20)]
        emptyData = []
        self._createdb(self.db, schema)
        self._createdb(testdb, schema, emptyData)

        heal_metric(self.db, testdb)

        original_data = whisper.fetch(self.db, 0)
        filled_data = whisper.fetch(testdb, 0)
        self.assertEqual(original_data, filled_data)

        # Heal again, should still be equal
        heal_metric(self.db, testdb)
        filled_data = whisper.fetch(testdb, 0)
        self.assertEqual(original_data, filled_data)

return

    # we want to retain as much precision as we can, hence we do backwards
    # walk in time

    # skip forward at max 'step' points at a time
    for archive in srcArchives:
        # skip over archives that don't have any data points
        rtime = time.time() - archive['retention']
        if tstop <= rtime:
            continue

        untilTime = tstop
        fromTime = rtime if rtime > tstart else tstart

        (timeInfo, values) = whisper.fetch(src, fromTime, untilTime)
        (start, end, archive_step) = timeInfo
        pointsToWrite = list(filter(
            lambda points: points[1] is not None,
            zip(range(start, end, archive_step), values)))
        # order points by timestamp, newest first
        pointsToWrite.sort(key=lambda p: p[0], reverse=True)
        whisper.update_many(dst, pointsToWrite)

        tstop = fromTime

        # can stop when there's nothing to fetch any more
        if tstart == tstop:
            return

def fill_archives(src, dst, startFrom):
    header = whisper.info(dst)
    archives = header['archives']
    archives = sorted(archives, key=lambda t: t['retention'])

    for archive in archives:
        fromTime = time.time() - archive['retention']
        if fromTime >= startFrom:
            continue

        (timeInfo, values) = whisper.fetch(dst, fromTime, startFrom)
        (start, end, step) = timeInfo
        gapstart = None
        for v in values:
            if not v and not gapstart:
                gapstart = start
            elif v and gapstart:
                # ignore single units lost
                if (start - gapstart) > archive['secondsPerPoint']:
                    fill(src, dst, gapstart - step, start)
                gapstart = None
            elif gapstart and start == end - step:
                fill(src, dst, gapstart - step, start)

            start += step

        startFrom = fromTime