def get_primary_dep(config, dep_tasks):
    """Find the dependent task to inherit attributes from.
    If ``primary-dependency`` is defined in ``kind.yml`` and is a string,
    then find the first dep with that task kind and return it. If it is
    defined and is a list, the first kind in that list with a matching dep
    is the primary dependency. If it's undefined, return the first dep.
    """
    primary_dependencies = config.get('primary-dependency')
    if isinstance(primary_dependencies, str):
        primary_dependencies = [primary_dependencies]
    if not primary_dependencies:
        assert len(dep_tasks) == 1, "Must define a primary-dependency!"
        return dep_tasks.values()[0]
    primary_dep = None
    for primary_kind in primary_dependencies:
        for dep_kind in dep_tasks:
            if dep_kind == primary_kind:
                assert primary_dep is None, \
                    "Too many primary dependent tasks in dep_tasks: {}!".format(
                        [t.label for t in dep_tasks]
                    )
                primary_dep = dep_tasks[dep_kind]
    if primary_dep is None:
        raise Exception("Can't find dependency of {}: {}".format(
            config['primary-dependency'], config
        ))
    return primary_dep