template-specialize

template-specialize is a command-line tool for rendering Jinja2 templates.

Render a Template File

For example, consider this Markdown name tag template, "nametag.md":

## Hello, my name is

# {{name}}
{% if title is defined %}
### {{title}}
{% endif %}

To render the template, execute template-specialize as follows:

$ template-specialize nametag.md nametag-roy.md -k name 'Roy Hobbs' -k title 'The best there ever was'

Afterward, the output file contains the rendered template:

## Hello, my name is

# Roy Hobbs

### The best there ever was

Render a Directory Template

You can also render directories of templates to an output directory:

$ template-specialize template/ output/ -k name value

Built-In Template Variables

The following template variables are always defined:

• now - the current datetime object

Environment Files

template-specialize was originally created to "specialize" web service configuration files for different runtime environments. Environment files are JSON files that allow for the definition of inheritable, structured template configuration values. Consider the following environments file:

{
    "base": {
        "values": {
            "service_name": "my-service"
        }
    },
    "test_base": {
        "parents": ["base"],
        "values": {
            "db_host": "test-db-host"
        }
    },

    // The test environment
    "test": {
        "parents": ["test_base"],
        "values": {
            "db_name": "test-db"
        }
    },

    // The live/production environment
    "live": {
        "parents": ["base"],
        "values": {
            "db_host": "live-db-host",
            "db_name": "live-db"
        }
    }
}

To render a template file using an environment, specify the environment file (or files) and the environment name with which to render the template:

$ template-specialize config-template.json config.json -c environments.json -e test

To view the template configuration data use the "--dump" argument:

$ template-specialize config-template.json config.json -c environments.json -e test --dump
{
    "db_host": "test-db-host",
    "db_name": "test-db",
    "service_name": "my-service"
}

Renaming and Deleting Output Files

When specializing a template directory, it is sometimes necessary to rename an output file or directory. For example, consider a Python project template with the following structure:

.
|-- README.md
|-- package-name.txt
|-- pyproject.toml
`-- src
    |-- __init__.py
    |-- package_name
    |   |-- __init__.py
    |   `-- package_name.py
    `-- tests
        |-- __init__.py
        `-- test_package_name.py

As part of the specialization, we'd like to rename the "package_name" directory, the "package_name.py" file, and the "test_package_name.py" file to the specialized package name. To accomplish this, we add the "package-name.txt' utility file and call the "template_specialize_rename" Jinja2 extension:

{# Rename template files #}
{% template_specialize_rename 'src/tests/test_package_name.py', 'test_' + package_name + '.py' %}
{% template_specialize_rename 'src/package_name/package_name.py', package_name + '.py' %}
{% template_specialize_rename 'src/package_name', package_name %}

{# Delete the package-name.txt utility template file #}
{% template_specialize_rename 'package-name.txt' %}

First, the "template_specialize_rename" extension is used to rename the package output files and directories. Finally, since we don't want the empty utility file in the output, we delete it using the "template_specialize_rename" extension with no second argument. Here's an example usage of our Python project template:

$ template-specialize python-package my-package -k package_name my_package

This command produces the following specialized template output with appropriately named package source directory and source files:

.
|-- README.md
|-- pyproject.toml
`-- src
    |-- __init__.py
    |-- my_package
    |   |-- __init__.py
    |   `-- my_package.py
    `-- tests
        |-- __init__.py
        `-- test_my_package.py

AWS Parameter Store

template-specialize can retrieve template values from AWS Parameter Store using botocore.

Here's an example of a JSON configuration file with a Parameter Store secret:

{
    "my_secret": {% filter tojson %}{% aws_parameter_store 'parameter-name' %}{% endfilter %}
}

botocore is usually configured using environment variables.

Usage

usage: template-specialize [-h] [-c FILE] [-e ENV] [-k KEY VALUE] [--dump]
                           SRC DST

positional arguments:
  SRC                   the source template file or directory
  DST                   the destination file or directory

options:
  -h, --help            show this help message and exit
  -c FILE               the environment files
  -e ENV                the environment name
  -k KEY VALUE, --key KEY VALUE
                        add a template key and value
  --dump                dump the template variables

Development

This package is developed using python-build. It was started using python-template as follows:

template-specialize python-template/template/ template-specialize/ -k package template-specialize -k name 'Craig A. Hobbs' -k email 'craigahobbs@gmail.com' -k github 'craigahobbs' -k noapi 1