Fixed #21179 -- Added a StreamingHttpResponse example for CSV files.

.. _`csv module's examples section`: http://docs.python.org/library/csv.html#examples

.. _`python-unicodecsv module`: https://github.com/jdunck/python-unicodecsv

.. _streaming-csv-files:

Streaming large CSV files

~~~~~~~~~~~~~~~~~~~~~~~~~

When dealing with views that generate very large responses, you might want to

consider using Django's :class:`~django.http.StreamingHttpResponse` instead.

For example, by streaming a file that takes a long time to generate you can

avoid a load balancer dropping a connection that might have otherwise timed out

while the server was generating the response.

In this example, we make full use of Python generators to efficiently handle

the assembly and transmission of a large CSV file::

    import csv

    from django.utils.six.moves import range

    from django.http import StreamingHttpResponse

    class Echo(object):

        """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 some_streaming_csv_view(request):

        """A view that streams a large CSV file."""

        # Generate a sequence of rows. The range is based on the maximum number of

        # rows that can be handled by a single sheet in most spreadsheet

        # applications.

        rows = (["Row {0}".format(idx), str(idx)] for idx in range(65536))

        pseudo_buffer = Echo()

        writer = csv.writer(pseudo_buffer)

        response = StreamingHttpResponse((writer.writerow(row) for row in rows),

                                         content_type="text/csv")

        response['Content-Disposition'] = 'attachment; filename="somefilename.csv"'

        return response

Using the template system

=========================

The :class:`StreamingHttpResponse` class is used to stream a response from

Django to the browser. You might want to do this if generating the response

takes too long or uses too much memory. For instance, it's useful for

generating large CSV files.

:ref:`generating large CSV files <streaming-csv-files>`.

.. admonition:: Performance considerations