https://github.com/peterjclaw/layer-loader

Easy composition of configuration files
https://github.com/peterjclaw/layer-loader

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Easy composition of configuration files

• Host: GitHub
• URL: https://github.com/peterjclaw/layer-loader
• Owner: PeterJCLaw
• License: mit
• Created: 2020-01-26T19:29:23.000Z (almost 5 years ago)
• Default Branch: master
• Last Pushed: 2020-07-21T20:25:42.000Z (over 4 years ago)
• Last Synced: 2024-09-08T09:13:52.985Z (2 months ago)
• Language: Python
• Homepage:
• Size: 36.1 KB
• Stars: 0
• Watchers: 3
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
# Layer-Loader

[![CircleCI](https://circleci.com/gh/PeterJCLaw/layer-loader.svg?style=svg)](https://circleci.com/gh/PeterJCLaw/layer-loader)

Layer-loader is a Python library designed to allow easy composition of configuration files.

This project was inspired by [hiera][puppet-hiera], though intends to be somewhat simpler.

[puppet-hiera]: https://puppet.com/docs/puppet/latest/hiera_intro.html

## Usage

The primary interface is a Python API:

``` python

import json

import layer_loader

data = layer_loader.load_files(

    ['dev.json', 'main.json'],

    loader=json.load,

)

```

This will load the data from `dev.json` and `main.json`, interpreting it as JSON,

combine it into a single object and then any placeholders are expanded.

For convenience you can also run `layer_loader` as a module:

```shell

$ cat dev.json

{

    "url": "http://localhost:8000"

}

$ cat main.json

{

    "endpoints": [

        "{url}/abc",

        "{url}/def",

        "{url}/ghi"

    ],

    "url": "https://production.system"

}

$ python -m layer_loader --loader=json.load dev.json main.json

{

    "endpoints": [

        "http://localhost:8000/abc",

        "http://localhost:8000/def",

        "http://localhost:8000/ghi"

    ],

    "url": "http://localhost:8000"

}

```

## Layers

Layers are specified in order from most important (top) to least important (bottom).

When combining layers, layer-loader uses the following rules:

* Mappings can be _merged_, combining the entries from several layers

* Scalar values and lists _replace_ entries in the lower layers

* Keys in more important layers override those in lower layers

* Where keys are present in multiple layers, it is an error for those

  keys to have values of different types. The exception to this is

  that keys can explicitly be set to `null` in a higher layer in order

  to remove a value set in a lower layer.

## Placeholders

Placeholders are specified similarly to python format strings and may appear

anywhere inside a string value, for example `'foo {place.holder} bar'`.

Placeholders should not appear in keys -- they will not be found there.

Placeholders are expanded by walking the flattened data structure, using dots in

the placeholder to separate names at each level of nesting.

There is no mechanism to specify which layer a placeholder should be looked up

within -- all placeholder expansion happens after the layers have been

flattened.