YAML Loader with include constructor (Python 3)

bar.yaml

- 3.6
- [1, 2, 3]

foo.yaml

a: 1
b:
    - 1.43
    - 543.55
c: !include bar.yaml

LICENSE.md

MIT License

Copyright (c) 2018 Josh Bode

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

loader.py

import os
import json

import yaml
from typing import Any, IO


class Loader(yaml.SafeLoader):
    """YAML Loader with `!include` constructor."""

    def __init__(self, stream: IO) -> None:
        """Initialise Loader."""

        try:
            self._root = os.path.split(stream.name)[0]
        except AttributeError:
            self._root = os.path.curdir

        super().__init__(stream)


def construct_include(loader: Loader, node: yaml.Node) -> Any:
    """Include file referenced at node."""

    filename = os.path.abspath(os.path.join(loader._root, loader.construct_scalar(node)))
    extension = os.path.splitext(filename)[1].lstrip('.')

    with open(filename, 'r') as f:
        if extension in ('yaml', 'yml'):
            return yaml.load(f, Loader)
        elif extension in ('json', ):
            return json.load(f)
        else:
            return ''.join(f.readlines())


yaml.add_constructor('!include', construct_include, Loader)


if __name__ == '__main__':
    with open('foo.yaml', 'r') as f:
        data = yaml.load(f, Loader)
    print(data)

It doesn't work in root node when combining with other nodes. For example:

!include include-test.yaml
specific_var: "xxx"

It throws an error:

ScannerError: mapping values are not allowed here