sw.py

#!/usr/bin/env nix-shell
#! nix-shell -i python -p pythonPackages.attrs pythonPackages.pyyaml

import attr

import yaml

@attr.s(frozen=True, slots=True)
class Subject(object):
    name = attr.ib()
    observations = attr.ib()

    def glue(self, other):
        name = self.name
        if name != other.name:
            name += " AKA " + other.name
        observations = self.observations.copy()
        for k, theirs in other.observations.iteritems():
            if k in observations:
                ours = observations[k]
                if ours != theirs:
                    raise Exception("ours != theirs")
            else:
                observations[k] = theirs
        return Subject(name=name, observations=observations)

@attr.s(frozen=True, slots=True)
class Story(object):
    names = attr.ib()
    subjects = attr.ib()

    @classmethod
    def from_dict(cls, **kwargs):
        names = [kwargs.pop("name")]
        subjects = kwargs.pop("subjects")
        subjects = {s["name"]: Subject(**s) for s in subjects}
        return cls(names=names, subjects=subjects, **kwargs)

    def glue(self, other):
        names = self.names + other.names
        subjects = {}
        keys = set(self.subjects.keys() + other.subjects.keys())
        for key in keys:
            ours = self.subjects.get(key)
            theirs = other.subjects.get(key)
            if ours is None:
                subjects[key] = theirs
            elif theirs is None:
                subjects[key] = ours
            else:
                subjects[key] = ours.glue(theirs)
        return Story(names=names, subjects=subjects)

def find_global_section(stories):
    story = Story(names=["The Null Story"], subjects={})
    for s in stories.itervalues():
        story = story.glue(s)
    return story

with open("sw.yaml") as handle:
    stories = yaml.safe_load(handle.read())

stories = {s["name"]: Story.from_dict(**s) for s in stories}
print find_global_section(stories)

sw.yaml

- name: A New Hope
  subjects:
    - name: Death Star
      observations:
        destroyed: 0
    - name: Obi-Wan Kenobi
      observations:
        died: 0
    - name: Luke Skywalker
      observations:
        rogue: 0
- name: Return of the Jedi
  subjects:
    - name: Obi-Wan Kenobi
      observations:
        ghost: 4
    - name: Luke Skywalker
      observations:
        jedi_knight: 4