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Django2.0手册:Outputting CSV with Django

Django2.0手册 AI君 125℃

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.

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.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)
    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 Context, loader

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.

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