前言：django在的orm下的choices怎么分组展示
from django.db.models import Count
books_by_language = Book.objects.values('language').annotate(num_books=Count('id'))
languages = dict(Book.LANGUAGE_CHOICES)
for book in books_by_language:
language = languages[book['language']]
num_books = book['num_books']
print(language, num_books)