158 lines
5.7 KiB
Plaintext
158 lines
5.7 KiB
Plaintext
===========================
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Outputting PDFs with Django
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===========================
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This document explains how to output PDF files dynamically using Django views.
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This is made possible by the excellent, open-source ReportLab_ Python PDF
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library.
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The advantage of generating PDF files dynamically is that you can create
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customized PDFs for different purposes -- say, for different users or different
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pieces of content.
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For example, Django was used at kusports.com_ to generate customized,
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printer-friendly NCAA tournament brackets, as PDF files, for people
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participating in a March Madness contest.
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.. _ReportLab: http://www.reportlab.com/opensource/
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.. _kusports.com: http://www.kusports.com/
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Install ReportLab
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=================
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The ReportLab library is `available on PyPI`_. A `user guide`_ (not
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coincidentally, a PDF file) is also available for download.
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You can install ReportLab with ``pip``:
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.. code-block:: console
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$ pip install reportlab
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Test your installation by importing it in the Python interactive interpreter::
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>>> import reportlab
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If that command doesn't raise any errors, the installation worked.
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.. _available on PyPI: https://pypi.python.org/pypi/reportlab
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.. _user guide: http://www.reportlab.com/docs/reportlab-userguide.pdf
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Write your view
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===============
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The key to generating PDFs dynamically with Django is that the ReportLab API
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acts on file-like objects, and Django's :class:`~django.http.HttpResponse`
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objects are file-like objects.
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Here's a "Hello World" example::
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from reportlab.pdfgen import canvas
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from django.http import HttpResponse
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def some_view(request):
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# Create the HttpResponse object with the appropriate PDF headers.
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response = HttpResponse(content_type='application/pdf')
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response['Content-Disposition'] = 'attachment; filename="somefilename.pdf"'
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# Create the PDF object, using the response object as its "file."
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p = canvas.Canvas(response)
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# Draw things on the PDF. Here's where the PDF generation happens.
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# See the ReportLab documentation for the full list of functionality.
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p.drawString(100, 100, "Hello world.")
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# Close the PDF object cleanly, and we're done.
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p.showPage()
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p.save()
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return response
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The code and comments should be self-explanatory, but a few things deserve a
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mention:
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* The response gets a special MIME type, :mimetype:`application/pdf`. This
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tells browsers that the document is a PDF file, rather than an HTML file.
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If you leave this off, browsers will probably interpret the output as
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HTML, which would result in ugly, scary gobbledygook in the browser
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window.
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* The response gets an additional ``Content-Disposition`` header, which
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contains the name of the PDF file. This filename is arbitrary: Call it
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whatever you want. It'll be used by browsers in the "Save as..." dialog, etc.
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* The ``Content-Disposition`` header starts with ``'attachment; '`` in this
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example. This forces Web browsers to pop-up a dialog box
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prompting/confirming how to handle the document even if a default is set
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on the machine. If you leave off ``'attachment;'``, browsers will handle
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the PDF using whatever program/plugin they've been configured to use for
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PDFs. Here's what that code would look like::
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response['Content-Disposition'] = 'filename="somefilename.pdf"'
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* Hooking into the ReportLab API is easy: Just pass ``response`` as the
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first argument to ``canvas.Canvas``. The ``Canvas`` class expects a
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file-like object, and :class:`~django.http.HttpResponse` objects fit the
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bill.
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* Note that all subsequent PDF-generation methods are called on the PDF
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object (in this case, ``p``) -- not on ``response``.
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* Finally, it's important to call ``showPage()`` and ``save()`` on the PDF
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file.
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.. note::
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ReportLab is not thread-safe. Some of our users have reported odd issues
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with building PDF-generating Django views that are accessed by many people
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at the same time.
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Complex PDFs
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============
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If you're creating a complex PDF document with ReportLab, consider using the
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:mod:`io` library as a temporary holding place for your PDF file. This
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library provides a file-like object interface that is particularly efficient.
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Here's the above "Hello World" example rewritten to use :mod:`io`::
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from io import BytesIO
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from reportlab.pdfgen import canvas
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from django.http import HttpResponse
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def some_view(request):
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# Create the HttpResponse object with the appropriate PDF headers.
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response = HttpResponse(content_type='application/pdf')
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response['Content-Disposition'] = 'attachment; filename="somefilename.pdf"'
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buffer = BytesIO()
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# Create the PDF object, using the BytesIO object as its "file."
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p = canvas.Canvas(buffer)
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# Draw things on the PDF. Here's where the PDF generation happens.
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# See the ReportLab documentation for the full list of functionality.
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p.drawString(100, 100, "Hello world.")
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# Close the PDF object cleanly.
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p.showPage()
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p.save()
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# Get the value of the BytesIO buffer and write it to the response.
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pdf = buffer.getvalue()
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buffer.close()
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response.write(pdf)
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return response
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Other formats
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=============
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Notice that there isn't a lot in these examples that's PDF-specific -- just the
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bits using ``reportlab``. You can use a similar technique to generate any
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arbitrary format that you can find a Python library for. Also see
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:doc:`/howto/outputting-csv` for another example and some techniques you can use
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when generated text-based formats.
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.. seealso::
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Django Packages provides a `comparison of packages
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<https://djangopackages.org/grids/g/pdf/>`_ that help generate PDF files
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from Django.
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