# Django 1.11.dev20170112000130 documentation

# 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.

## 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.

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(content_type='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 MIME type, 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...” dialog, 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.

Handling Unicode on Python 2

Python 2’s `csv` module does not support Unicode input. Since Django uses Unicode internally this means strings read from sources such as `HttpRequest` are potentially problematic. There are a few options for handling this:

- Manually encode all Unicode objects to a compatible encoding.
- Use the `UnicodeWriter` class provided in the csv module’s examples section.
- Use the python-unicodecsv module, which aims to be a drop-in replacement for `csv` that gracefully handles Unicode.

For more information, see the Python documentation of the `csv` module.

### Streaming large CSV files

When dealing with views that generate very large responses, you might want to consider using Django’s `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 {}".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

Alternatively, you can use the Django template system to generate CSV. This is lower-level than using the convenient Python `csv` module, 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(content_type='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 `content_type='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.

## Other text-based formats

Notice that there isn’t very much specific to CSV here – just the specific output format. You can use either of these techniques to output any text-based format you can dream of. You can also use a similar technique to generate arbitrary binary data; see Outputting PDFs with Django for an example.