Словарь, состоящий из словарей, и способы извлечения данных из него на Python

>>> books = {}
>>> books['physics'] = dict(author='Громов',lvl=7,q='good')
>>> books['math'] = dict(author='Asimov',lvl=7,q='mid')
>>> books['biology'] = dict(author='Smogin',lvl=10,q='mid')
>>> books
{'biology': {'q': 'mid', 'lvl': 10, 'author': 'Smogin'}, 'physics': {'q': 'good', 'lvl': 7, 'author': 'Громов'}, 'math': {'q': 'mid', 'lvl': 7, 'author': 'Asimov'}}
>>> import pprint
>>> pprint.pprint(books)
{'biology': {'author': 'Smogin', 'lvl': 10, 'q': 'mid'},
 'math': {'author': 'Asimov', 'lvl': 7, 'q': 'mid'},
 'physics': {'author': 'Громов', 'lvl': 7, 'q': 'good'}}

>>> books['biology']['author']
'Smogin'
>>> for i in books:
...     print(i)
... 
biology
physics
math
>>> for i in books:
...     print(books[i]['lvl'])
... 
10
7
7