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