configtpl

This library builds configuration in two stages:

1. Renders the provided configuration as Jinja templates
2. Parses the rendered data as file with the specified format

Features

• Uses Jinja2 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:

Functions

See also List of Global Functions on Jinja page

Precendence

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

Examples

You try run this example in the docs/examples/readme directory by running the run.sh script.

The functional tests folder might be useful for more examples.

A very simple example of usage is provided below: This example uses YAML format which requires the yaml extra to be installed.

# 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
param1_rev: "{{ app.param1 | str_rev }}"
param1_duplicated: "{{ str_duplicate(app.param1, 3) }}"

# app.py
import json

from configtpl.main import ConfigTpl, ConfigFormat


def filter_str_rev(value: str) -> str:
  return value[::-1]


def function_str_duplicate(value: str, n_times: int) -> str:
  return value * n_times


builder = ConfigTpl(
  defaults={"default": "default_value"},
  env_var_prefix="MY_APP",
  jinja_globals={
    "str_duplicate": function_str_duplicate,
  },
  jinja_filters={
    "str_rev": filter_str_rev,
  },
)
cfg = builder.build_from_files(
  paths=["my_first_config.cfg", "my_second_config.cfg"],
  overrides={"override": "overridden"},
  file_type=ConfigFormat.YAML,
)
print(json.dumps(cfg, indent=2))  # noqa: T201

# Execution

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

# output
{
  "default": "default_value",
  "app": {
    "param_env": "testing",
    "param1": "abc",
    "param2": "def",
    "param3": "abc123"
  },
  "hash": "900150983cd24fb0d6963f7d28e17f72",
  "override": "overridden",
  "param1_rev": "cba",
  "param1_duplicated": "abcabcabc",
  "nested": {
    "var": "hello"
  }
}