How to include a YAML file inside another

The easiest and purest method without relying on C headers is PyYaml (documentation), which can be installed via pip install pyyaml:

#!/usr/bin/env python

import yaml

with open("example.yaml", "r") as stream:
    try:
        print(yaml.safe_load(stream))
    except yaml.YAMLError as exc:
        print(exc)

And that's it. A plain yaml.load() function also exists, but yaml.safe_load() should always be preferred unless you explicitly need the arbitrary object serialization/deserialization provided in order to avoid introducing the possibility for arbitrary code execution.

Note the PyYaml project supports versions up through the YAML 1.1 specification. If YAML 1.2 specification support is needed, see ruamel.yaml as noted in this answer.

Also, you could also use a drop in replacement for pyyaml, that keeps your yaml file ordered the same way you had it, called oyaml. View synk of oyaml here

I don't think it is possible. You can reuse "node" but not part of it.

bill-to: &id001
    given  : Chris
    family : Dumars
ship-to: *id001

This is perfectly valid YAML and fields given and family are reused in ship-to block. You can reuse a scalar node the same way but there's no way you can change what's inside and add that last part of a path to it from inside YAML.

If repetition bother you that much I suggest to make your application aware of root property and add it to every path that looks relative not absolute.