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)

This is great, thanks!
Is there a license for this?

Hi @MaximilianR - I haven't put anything up in terms of a license, but I'd consider this to be under the MIT license.
Edit: license added

Nice. Would be nice to have an example of use, too.

Hi @petri - just saw your comment (I don't get notifications) - example added!

Yaml overload:

myyaml.py:

import yaml
from yaml import *
import logging
import os.path
import functools


log = logging.getLogger(__name__)


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())


# Set MyLoader as default.
load = functools.partial(yaml.load, Loader=ExtLoader)

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

myyaml_usage.py:

import myyaml as yaml


def normal(filename):
    """Normal usage."""

    with open(filename, 'r') as f:
        data = yaml.load(f)
    return data


def std_loader(filename):
    """Std yaml loader support."""

    with open(filename, 'r') as f:
        data = yaml.load(f, Loader=yaml.Loader)
    return data


if __name__ == '__main__':
    print('Normal:\n{}\n'.format(
        normal('foo.yaml')))
    print('Std loader (bar.yaml):\n{}\n'.format(
        std_loader('bar.yaml')))
    try:
        std_loader('foo.yaml')
    except yaml.constructor.ConstructorError as e:
        print('Std loader tag error (foo.yaml):\n{}\n'.format(e))

Is there a way to get a reference to the parent tag? Ive tried looking around the calling data structure but cannot see obvious.

ie in yaml file
myKey: !include myYaml.yml

I would like to get string myKey in the construct_include function

@atomlin - I'm not sure of a way to get this from the loader directly as there appears to be little context available by the time the include constructor is called, but you could do something like this:

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

    mark = node.start_mark
    with open(os.path.join(loader._root, loader.name), "rt") as source:
        for _ in range(mark.line + 1):
            line = source.readline()

        tag = re.search(r"""(['"])?([^'"]+)(['"])?:$""", line[:mark.column].rstrip())
        if tag is not None:
            open, tag, close = tag.groups()
            if open != close:  # if tag is quoted, match quotes
                tag = None
        else:
            tag = None

    ## do something with tag ##
    ...

    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())

(it's a bit hacky, though :)

Is there a way for the anchors in the imported file to still maintain anchor status?

@atrifex do you mean something like this:

# bar.yaml
y: &y
  a: 1
  b: 2

# foo.yaml
x: !include bar.yaml
z:
  <<: *y
  b: 20

I think the answer is: probably not, without some additional work :)

yep, that's what I meant.

That's fair. Will link if I end up implementing it.

OK - if you do, that would be great :)

One thing that's going to complicate this is that I believe the loader tries to resolve anchors before resolving tags

yep, seems like its not possible so far.

Too bad. Could have pulled out a lot of duplicate configs and shared them across files. Honestly surprised that some of these things are not supported by default.

Has anyone used a schema validation tool (such as Yamale) along with this custom constructor for include tags?

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