book2.py

#!/usr/bin/python3

import json
import requests

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

r = requests.get('https://www.googleapis.com/books/v1/volumes?q=hobbit')
for book in r.json()['items']:
    print(get_by_keys(book, 'volumeInfo', 'industryIdentifiers', 0, 'identifier'))