# Django 5.2.9 - dokumentacja

# How to create CSV output

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.

## Wykorzystanie Pythonowej biblioteki do plików CSV

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.

Oto przykład:

    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",
            headers={"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.

- You can hook into the CSV-generation API by passing `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.

- 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. Pass `writerow()` your raw strings, and it’ll do the right thing.

### Strumienowanie dużych plików CSV

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.http import StreamingHttpResponse

    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 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)
        return StreamingHttpResponse(
            (writer.writerow(row) for row in rows),
            content_type="text/csv",
            headers={"Content-Disposition": 'attachment; filename="somefilename.csv"'},
        )

## Używanie systemu szablonów

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.

Oto przykład, który generuje taki sam plik CSV jak powyższy:

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

    def some_view(request):
        # Create the HttpResponse object with the appropriate CSV header.
        response = HttpResponse(
            content_type="text/csv",
            headers={"Content-Disposition": 'attachment; filename="somefilename.csv"'},
        )

        # The data is hardcoded 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 = {"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 short template 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.

## Inne formaty tekstowe

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 Jak tworzyć pliki PDF for an example.