Constant memory streaming CSV writer (works with prefetch_related too)

.py

def generator_from_queryset(queryset, chunksize=2000, enumerate=False):
    assert queryset.query.order_by is not None
    offset = 0
    i = 0
    finished = False
    while not finished:
        finished = True
        for row in queryset[offset:offset + chunksize]:
            finished = False
            if enumerate:
                yield i, row
                i = i + 1
            else:
                yield row
        offset = offset + chunksize

class Echo:
    """An object that implements just the write method of the file-like interface."""

    def write(self, value):
        """Write the value by returning it, instead of storing in a buffer."""
        return value

def write_csv_response(self, queryset):
    pseudo_buffer = Echo()
    writer = csv.writer(pseudo_buffer)

    data = generator_from_queryset(queryset, chunksize=500)

    generator = itertools.chain(
        (writer.writerow(self.get_headers()) for _ in range(1)),
        (writer.writerow(self.to_csv_row(item)) for item in data)
    )

    response = StreamingHttpResponse(generator, content_type="text/csv")
    response['Content-Disposition'] = 'attachment; filename="{}.csv"'.format(self.filename)
    return response