def nested_lookup(key, document):
    """Lookup a key in a nested document, return a list of values"""
    return list(_nested_lookup(key, document))

def _nested_lookup(key, document):
    """Lookup a key in a nested document, yield a value"""
    if isinstance(document, list):
        for d in document:
            for result in _nested_lookup(key, d):
                yield result

    if isinstance(document, dict):
        for k, v in document.items():
            if k == key:
                yield v
            elif isinstance(v, dict):
                for result in _nested_lookup(key, v):
                    yield result
            elif isinstance(v, list):
                for d in v:
                    for result in _nested_lookup(key, d):
                        yield result