book.py

def get_by_keys(res, *keys):
    try:
        for k in keys:
            res = res[k]
        return res
    except (TypeError, KeyError, IndexError):
        return None

book_data = {
    'title': get_by_keys(result, 'volumeInfo', 'title'),
    'authors': get_by_keys(result, 'volumeInfo', 'authors', 0),
    'publish_date': get_by_keys(result, 'volumeInfo', 'publishedDate'),
    ...
}