Creating PDFs with LaTeX and Django

When I started at my new job, the first task was: reports. It was a good way to learn the codebase, but when I opened the file that generated the PDFs, I found something really messed up. Every element (columns, rows, title…) had its position defined by hand, in centimeters. So a task that should have been quick was going to take much longer.

But I remembered that LaTeX can easily create PDFs. Could I use it with Django? That way I could describe the structure of the document and leave the layout to LaTeX, instead of counting centimeters.

So I found django-tex , a simple Django app to render LaTeX templates and compile them into PDF files. You just need a local LaTeX installation and the Jinja2 templating engine for template rendering. In my case, I forked the project and added some escape characters and filters for templates.

Setup

• Install it. What’s on PyPI is the original; use my fork if you want the extra filters:

pip install django-tex
# or: pip install git+https://github.com/gabicavalcante/django-tex

• Add django_tex to your INSTALLED_APPS setting:

INSTALLED_APPS = [
    ...
    'django_tex',
]

• Add a second template backend for your .tex files. It sits alongside the HTML backend you already have, so keep both entries in TEMPLATES. ROOT_PATH below is just a variable pointing at the project root, so use whatever your settings.py already uses for paths:

TEMPLATES = [
    {
        'NAME': 'tex',
        'BACKEND': 'django_tex.engine.TeXEngine',
        'APP_DIRS': True,
        'DIRS': [
            '%s/templates' % ROOT_PATH
        ],
    },
]

• Create a LaTeX template test.tex in your template directory:

\documentclass{article}
\begin{document}
\section{ {{- title -}} }
\end{document}

Both details in that \section line matter. The dashes in {{- title -}} strip the whitespace around the value, so you get \section{Title} instead of \section{ Title }. The spaces are what keep Jinja from reading {{{ as the start of an expression followed by a stray brace.

Rendering

There are two ways to get the PDF out. compile_template_to_pdf gives you the file as a bytes object:

from django_tex.core import compile_template_to_pdf

template_name = 'test.tex'
context = {'title': 'Test PDF File'}
PDF = compile_template_to_pdf(template_name, context)

render_to_pdf wraps that in an HttpResponse, which is what you want from a view:

from django_tex.shortcuts import render_to_pdf

def view(request):
    template_name = 'test.tex'
    context = {'title': 'Test PDF File'}
    return render_to_pdf(request, template_name, context,
                filename='test.pdf')

The default LaTeX interpreter is lualatex, but you can change it with the LATEX_INTERPRETER setting, for instance: LATEX_INTERPRETER = 'pdflatex'. Whichever one you pick has to be installed on the machine that runs the compile, which is worth remembering when you deploy.

I did end up refactoring the reports to LaTeX templates, and generating a PDF came down to a few seconds. The bigger win was that a new report became a template I could read, instead of a list of coordinates.