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Jinja-style templating for LaTeX documents by Curvenote

Project description

JTEX

JTEX is a command line tool (CLI) for rendering LaTeX documents from jinja-style templates. This package uses Jinja2 as the template engine with a modified environment and syntax that plays well with LaTeX's markup.

This allows you to build LaTeX documents driven by content, data and a template. We built this package while developing our template based PDF/LaTeX export system for Curvenote, where it is used to create documents from the templates on the Curvenote Community Template Repo.

A CHANGE LOG is available here.

Installation

Install the package into your virtual environment using pip:

  pip install jtex

and confirm correct installation by typing:

  jtex --version

An example

As we are dealing with content and data, the cli accepts paths to specific files or folders rather than accepting arguments inline. Here is a minimal example:

Given these 2 files:

% content.tex
% ---
% title: Exploring Outer Space
% author:
%   name: Ana Space
%   email: ana@outer.space
% ---
Outer space is the expanse that exists beyond Earth and between celestial bodies. Outer space is not completely empty—it is a hard vacuum containing a low density of particles, predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, neutrinos, dust, and cosmic rays.

content.tex contains a front matter section (a header comment block delimited by % ---) and the body of content itself. Front matter contains a yaml formatted data structure that is made available in the template rendering namespace, such that each top level key is a variable at global scope, as shown in template.tex below.

% template.tex
\documentclass{article}

\title{[-title-]}
\author{[-author.name-] ([-author.email-])}

\begin{document}
\maketitle

[-CONTENT-]
\vskip 1cm
The End!
\end{document}

We can render a LaTeX document with the following command:

  jtex freeform output.tex data.yml content.tex template.tex

To produce a .tex file with the following contents:

% output.tex
% ---
% title: Exploring Outer Space
% author:
%   name: Ana Space
%   email: ana@outer.space
% ---
\documentclass{article}

\title{Exploring Outer Space}
\author{Ana Space (ana@outer.space)}

\begin{document}
\maketitle

% content.tex
Outer space is the expanse that exists beyond Earth and between celestial bodies. Outer space is not completely empty—it is a hard vacuum containing a low density of particles, predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, neutrinos, dust, and cosmic rays.
\vskip 1cm
The End!
\end{document}

Which when compiled produces the following document:

The document layout is flexible and will be based on structure provided in the template.tex file, where the modified jinja syntax ([-, -]) is used to expand variables from the matching DocModel provided in data.yml.

[-CONTENT-] is a special variable that will expand to the entire contents of content.tex ()

This example only shows variable expansion ([-myvar-]) but the full jinja2 environment is available with control flow, filters and many python commands.

The freeform command shown above is not opinionated and can be used to render any template with a matching DocModel data structure.

CLI Overview

Get help from the command line tool at any time using the --help option.

  jtex --help

Note: the CLI uses typer which provides shell completion option as standard. These are list in help messages and installation is recommended, but these commands are not central to use of the tool.

Command overview

The following commands are available on the cli.

freeform

freeform is an un-opinionated rendering command which as in the example above will allow you to render any template given content and a DocModel.

jtex freeform --help

Usage: jtex freeform [OPTIONS] TEMPLATE_TEX [CONTENT_TEX]

  Build a LaTeX document based on a free-form template, accompanying data
  structure and optional 'body' content. This can be used for general template
  rendering independently from Curvenote's prescriptive template structure. To
  build based on (and to develop/test) Curvenote templates use `build`.

Arguments:
  TEMPLATE_TEX   Path to a file with a compatible LaTeX template e.g.
                 mytemplate.tex. The template should align with the data
                 structure given by the DocModel  [required]
  CONTENT_TEX   Path to a file containing the content to render and jtex front
                matter.  [required]

Options:
  --output-tex FILE  Optional name of a local file to write the rendered
                     content to.This will override the data specified in the
                     front matter in content.
  --bib FILE         Path to an optional bib file. This will be copied as-is
                     into the target folder.
  --help             Show this message and exit.

The "DocModel" in this case is a bit of an overstatement as it is just a free-form python dictionary defined in the data.yml file as shown above.

As you build your template, you can decide on the structure of the data in this file and keep it aligned with the variables you access from within the template. To find out more see Creating Templates

render

render is an opinionated rendering command intended for use with Curvenote content and templates specifically.

jtex render --help

Usage: jtex render [OPTIONS] CONTENT_FILE

  Build a LaTeX document based on a Curvenote LaTeX Template, accompanying
  docmodel data structure and content. Can be used to develop/test Curvenote
  templates.

Arguments:
  CONTENT_FILE  Path to a .tex file with containing jtex front matter content
                to render.  [required]

Options:
  --output-path DIRECTORY    If supplied with override the jtex.output.path
                             (and default path) specified in front matterThis
                             is useful when dynamically setting a temporary
                             output folder.Will be created if it does not
                             exist.
  --template-path DIRECTORY  If supplied with override the jtex.template
                             option and use the template found on this path
  --help                     Show this message and exit.

When exporting LaTeX from Curvenote's API custom environments and commands are included by default. These require certain packages to be loaded and definitions to be included in the final document. render will include these definition files and expect certain structure to be present in the DocModel when rendering.

As render is not generally applicable outside of Curvenote templates, we'll not discuss the details further here. For more information check the Curvenote Open Template Repo.

Note: The Curvenote API can also respond with vanilla LaTeX, but this is not the default case for rendering. For more information on programmatically accessing the Curvenote API, see the Curvenote python client.

validate

validate is a dry run command which will validate a Curvenote template. This is very simple validation at the moment and we expect this to be extended.

jtex validate --help

Usage: jtex validate [OPTIONS] TEMPLATE_PATH

Arguments:
  TEMPLATE_PATH  Local folder containing the Curvenote compatible template to
                 validate  [required]

Creating Templates

This cli tool uses a customized jinja2 environment. We explain the custom syntax below and how to use that in conjunction with the content.tex and data.yml files in a bit more detail than shown in the previous example.

However, to get the most out of this tool, understanding how jinja2 works and the features it provides will help a lot. The Jinja Template Designer Documentation is a great resource, covering all the features of the jinja2 language in the context of HTML rendering and the standard jinja2 syntax.

That guide along with the information included below for LaTeX rendering and our custom syntax should give you everything you need to know to produce your own templates.

Jinja

About jinja templates:

A template contains variables and/or expressions, which get replaced with values when a template is rendered; and tags, which control the logic of the template. The template syntax is heavily inspired by Django and Python.

The cli uses a jinja2 environment with the following modifications.

Syntax

customized standard jinja2
Statements [# #] {% %}
Expressions [- -] {{ }}
Comments %# #% {# #}
Line Comment %% ##

A minimal LaTeX example illustrating these would be:

\documentclass{article}
\begin{document}
\section{Famous People}
%% Print a list of famous people defined in the context dictionary
\begin{itemize}
[# for person in famous_people #]
\item [-person.name-], [-person.job-] [# if person.email #]([-person.email-])[# endif #]
[# endfor #]
\end{itemize}
\end{document}

Which will print out a list of famous people's names, jobs and emails, if we have them.

Other environment differences

In addition to the custom syntax we also set the following options:

option our setting jinja default effect
trim_blocks True False If this is set to True the first newline after a block is removed (block, not variable tag!)
autoescape False True If set to False the XML/HTML autoescaping feature is disabled
auto_reload True False Will always check template location for changes and recompiles the template as needed
undefined SlientUndefined None Ignore any undefined variables in the template, render anyways without affected blocks or variables
keep_trailing_newline True False Preserve the trailing newline when rendering templates, important in LaTeX

jinja provide a whole host of functions, tests and filters at global scope. We have extended further this by adding the python __builtins__ providing additional commonly used python functions within the jinja rendering context.

Building a DocModel

We use the term DocModel to refer to the dictionary of data passed to a jinja template for rendering, loaded from front matter in the content file. jinja docs call this the Context Dictionary. It is easy to relate this to the yaml that you need to create to use the cli.

The fields at the root level of the strcture are available as variables in the jinja context at global scope.

# data.yml
title: Outer Space
author: Ana Cosmo

% template.tex
...
\title{[-title-]}
\author{[-author-]}
...

You can add comments to your template, and these will be removed at render time. Just in case, the comments are also valid LaTeX comments so should not affect your build even if one did leak through

  % template.tex

  % this is a LaTeX comment
  %# this is a template comment and will be removed at render, but it is also a valid LaTeX comment #%

These variables themselves can be nested data structures of dictionaries, lists, strings, numbers and booleans

# data.yml
authors:
  - name: Ana Cosmo
    email: ana@thecosmos.org
  - name: Bill Saturn
    email: bill@gasgiant.com
tags:
  - space
  - planets
  - cosmos

% template.tex
...
[# for author in authors #]
\author{[-author.name-] ([-author.email-])}
[# endfor #]

The first author is [-authors[0].name-]
The last author is [-authors[-1].name-]

tags: [-tags|join(', ')-]

%# main content goes here #%
[-CONTENT-]
...

[-CONTENT-] is a special variable that will expand to the entire contents of content.tex

We'll not go into more jinja features here, as they are covered in the Jinja Template Designer Documentation -- simply replace the standard jinja syntax with our customized syntax and bear in mind the rules of LaTeX and constructing sophisticated templates is pretty straightforward with practice.

Curvenote Templates

To look at some of the templates we've developed at Curvenote, or for documentation on how to create template for Curvenote please visit the Open Template Repo and check the documentation there.

We use this cli tool for development, testing and validation of any template submitted to that repo.

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