==========================
Outputting CSV with Django
==========================

This document explains how to output CSV (Comma Separated Values) dynamically
using Django views.

To do this, you can either use the `Python CSV library`_ or the Django template
system.

.. _Python CSV library: http://www.python.org/doc/current/lib/module-csv.html

Using the Python CSV library
============================

Python comes with a CSV library, ``csv``. The key to using it with Django is
that the ``csv`` module's CSV-creation capability acts on file-like objects,
and Django's ``HttpResponse`` objects are file-like objects.

.. admonition:: Note

    For more information on ``HttpResponse`` objects, see
    `Request and response objects`_.

    For more information on the CSV library, see the `CSV library docs`_.

    .. _Request and response objects: http://www.djangoproject.com/documentation/request_response/
    .. _CSV library docs: http://www.python.org/doc/current/lib/module-csv.html

Here's an example::

    import csv
    from django.http import HttpResponse

    def some_view(request):
        # Create the HttpResponse object with the appropriate CSV header.
        response = HttpResponse(mimetype='text/csv')
        response['Content-Disposition'] = 'attachment; filename=somefilename.csv'

        writer = csv.writer(response)
        writer.writerow(['First row', 'Foo', 'Bar', 'Baz'])
        writer.writerow(['Second row', 'A', 'B', 'C', '"Testing"', "Here's a quote"])

        return response

The code and comments should be self-explanatory, but a few things deserve a
mention:

    * The response gets a special mimetype, ``text/csv``. This tells
      browsers that the document is a CSV file, rather than an HTML file. If
      you leave this off, browsers will probably interpret the output as HTML,
      which will result in ugly, scary gobbledygook in the browser window.

    * The response gets an additional ``Content-Disposition`` header, which
      contains the name of the CSV file. This filename is arbitrary; call it
      whatever you want. It'll be used by browsers in the "Save as..."
      dialogue, etc.

    * Hooking into the CSV-generation API is easy: Just pass ``response`` as
      the first argument to ``csv.writer``. The ``csv.writer`` function expects
      a file-like object, and ``HttpResponse`` objects fit the bill.

    * For each row in your CSV file, call ``writer.writerow``, passing it an
      iterable object such as a list or tuple.

    * The CSV module takes care of quoting for you, so you don't have to worry
      about escaping strings with quotes or commas in them. Just pass
      ``writerow()`` your raw strings, and it'll do the right thing.

Using the template system
=========================

Alternatively, you can use the `Django template system`_ to generate CSV. This
is lower-level than using the convenient CSV, but the solution is presented
here for completeness.

The idea here is to pass a list of items to your template, and have the
template output the commas in a ``{% for %}`` loop.

Here's an example, which generates the same CSV file as above::

    from django.http import HttpResponse
    from django.template import loader, Context

    def some_view(request):
        # Create the HttpResponse object with the appropriate CSV header.
        response = HttpResponse(mimetype='text/csv')
        response['Content-Disposition'] = 'attachment; filename=somefilename.csv'

        # The data is hard-coded here, but you could load it from a database or
        # some other source.
        csv_data = (
            ('First row', 'Foo', 'Bar', 'Baz'),
            ('Second row', 'A', 'B', 'C', '"Testing"', "Here's a quote"),
        )

        t = loader.get_template('my_template_name.txt')
        c = Context({
            'data': csv_data,
        })
        response.write(t.render(c))
        return response

The only difference between this example and the previous example is that this
one uses template loading instead of the CSV module. The rest of the code --
such as the ``mimetype='text/csv'`` -- is the same.

Then, create the template ``my_template_name.txt``, with this template code::

    {% for row in data %}"{{ row.0|addslashes }}", "{{ row.1|addslashes }}", "{{ row.2|addslashes }}", "{{ row.3|addslashes }}", "{{ row.4|addslashes }}"
    {% endfor %}

This template is quite basic. It just iterates over the given data and displays
a line of CSV for each row. It uses the `addslashes template filter`_ to ensure
there aren't any problems with quotes. If you can be certain your data doesn't
have single or double quotes in it, you can remove the ``addslashes`` filters.

.. _Django template system: http://www.djangoproject.com/documentation/templates/
.. _addslashes template filter: http://www.djangoproject.com/documentation/templates/#addslashes
