rawl_loader.py

import yaml
import os.path


class ExtLoaderMeta(type):
    def __new__(metacls, __name__, __bases__, __dict__):
        """Add include constructer to class."""

        # register the include constructor on the class
        cls = super().__new__(metacls, __name__, __bases__, __dict__)
        cls.add_constructor("!include", cls.construct_include)

        return cls


class ExtLoader(yaml.Loader, metaclass=ExtLoaderMeta):
    """YAML Loader with `!include` constructor."""

    def __init__(self, stream):
        """Initialise Loader."""

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

        super().__init__(stream)

    def construct_include(self, node):
        """Include file referenced at node."""

        filename = os.path.abspath(
            os.path.join(self._root, self.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, ExtLoader)
            else:
                return "".join(f.readlines())