test.py

x = open('test.csv', 'w')

stream_labels = list(Stream.objects.order_by('label').values_list('label', flat=True))

x.write('Timestamp,' + ','.join(stream_labels) + '\n')

for timestamp in Data.objects.values_list('timestamp', flat=True):
  data_values = Data.objects.filter(timestamp=timestamp, stream__label__in=stream_labels).order_by('stream__label).values_list('data', flat=True)
  x.write(str(timestamp) + ',' + ','.join(data_values) + '\n')