Yaml construction

yaml_constructor.py

import pathlib

import yaml
from yaml.constructor import Constructor


class CustomConstructor(Constructor):
    def construct_yaml__secret(self, node):
        values = self.construct_mapping(node)
        username = values["username"]
        password = values["password"]
        return f"secret_{username}_{password}"

    def construct_yaml__file(self, node):
        filename = self.construct_scalar(node)
        file = pathlib.Path(filename)
        if not file.exists():
            return f"{node.value} not found!"
        with file.open(mode="r") as file:
            return file.read()

    def construct_yaml__user(self, node):
        users = self.construct_sequence(node)
        users = list(map(lambda it: f"{it}@mail.com", users))
        return users


def get_loader():
    loader = yaml.FullLoader
    loader.add_constructor("!file", CustomConstructor.construct_yaml__file)
    loader.add_constructor("!user", CustomConstructor.construct_yaml__user)
    loader.add_constructor("!secret", CustomConstructor.construct_yaml__secret)
    return loader


content = """
---
version: '2.7'
description: !file description.md
authors: !user
  - me
  - you
apikey: !secret
  username: test
  password: 123
"""
config = yaml.load(content, Loader=get_loader())

assert config == {
    "version": "2.7",
    "description": "description.md not found!",
    "authors": [
        "[email protected]",
        "[email protected]"
    ],
    "apikey": "secret_test_123"
}