configtpl 2.0.1

Configuration builder which combines features of Jinja and YAML

configtpl

This library builds configuration in two stages:

1. Renders the provided configuration as Jinja templates
2. Parses the rendered data as YAML file

Features

• Uses Jinja2 and Yaml capabilities to build a dynamic configuration
• Multiple configuration files might be passed. The library merges all of them into single config.
• Basic confuration includes Jinja functions and filters for general-purpose tasks:
  • Reading the environment variables
  • Execution of system commands
  • Hashing
• Reading parameters from environment variables
• Builds the configuration from files (build_from_files method) and from strinngs (build_from_str method)
• If the environment variable prefix is provided, merges the corresponding environment variables into the configuration.

Standard features

Filters

In addition to Jinja buildin filters, the library provides the following ones:

Filter	Description
base64	Base64 encoding
base64_decode	Base64 decoding
md5	MD5 hash
sha256	SHA-256 hash
sha512	SHA-512 hash
split_space	Splits a string with space separator into list of strings

Functions

See also List of Global Functions on Jinja page

Function	Description
cmd(cmd: str)	Executes a system command and returns the standard output
cwd()	Returns the current working directory
env(name: str, default: str)	Returns the value of enviroment variable name if it exists,
	or falls back to default value otherwise
file(path: str)	Reads the file and returns the contents
uuid	Generates a UUID e.g 1f6c868d-f9b7-4d3f-b7c9-48048b065019

Precendence

1. Defaults
2. Configuration from given files or string
3. Environment variables, if variable prefix is provided
4. Overrides

Examples

You can check the functional tests folder for more examples.

A very simple example of usage is provided below:

# my_first_config.cfg

{% set my_val = "abc" %}
app:
  param_env: "{{ env('MY_ENV_VAR', 'default') }}"
  param1: "{{ my_val }}"

# my_second_config.cfg
app:
  param2: def
  param3: "{{ app.param1 }}123"
hash: "{{ app.param1 | md5 }}"
override: test

# app.py

import json
from configtpl.main import ConfigTpl

builder = ConfigTpl(
  defaults={"default": "default_value"},
  env_var_prefix="MY_APP",
  overrides={"override": "overridden"},
)
cfg = builder.build_from_files(files=["my_first_config.cfg", "my_second_config.cfg"])
print(json.dumps(cfg, indent=2))

# Execution

MY_ENV_VAR=testing MY_APP__NESTED__VAR=hello python ./app.py

# output
{
  "app": {
    "param_env": "testing",
    "param1": "abc",
    "param2": "def",
    "param3": "abc123"
  },
  "default": "default_value",
  "hash": "900150983cd24fb0d6963f7d28e17f72",
  "nested": {
    "var": "hello"
  },
  "override": "overridden"
}