A safe way to read yml files with environmental variable integration

yml_reader.py

#!/usr/bin/env python

from os import environ
from re import compile

from yaml import SafeLoader, load


def yml(path=None, data=None, tag=None):
    """
    Load a yaml configuration file (path) or data object(data)
    and resolve any environment variables. The environment
    variables must be in this format to be parsed: ${VAR_NAME}.
    E.g.:
    database:
        host: ${HOST}
        port: ${PORT}
        ${KEY}: ${VALUE}
    app:
        log_path: '/var/${LOG_PATH}'
        something_else: '${AWESOME_ENV_VAR}/var/${A_SECOND_AWESOME_VAR}'
    :param str path: the path to the yaml file
    :param str data: the yaml data itself as a stream
    :param str tag: the tag to look for
    :return: the dict configuration
    :rtype: dict[str, T]
    """
    pattern = compile('.*?\${(\w+)}.*?')
    loader = SafeLoader
    loader.add_implicit_resolver(tag=tag, regexp=pattern, first=None)

    def env_var_constructor(loader, node):
        """
        Extracts the environment variable from the node's value
        :param yaml.Loader loader: the yaml loader
        :param node: the current node in the yaml
        :return: the parsed string that contains the value of the environment
        variable
        """
        value = loader.construct_scalar(node=node)
        match = pattern.findall(string=value)
        if match:
            full_value = value
            for g in match:
                full_value = full_value.replace(
                    f'${{{g}}}', environ.get(key=g, default=g))
            return full_value
        return value

    loader.add_constructor(tag=tag, constructor=env_var_constructor)

    if path:
        with open(path) as conf_data:
            return load(stream=conf_data, Loader=loader)
    elif data:
        return load(stream=data, Loader=loader)
    else:
        raise ValueError('Either a path or data should be defined as input')


yaml = yml("testing/yml.yml")
print(yaml)