定义一个产品类Book表示图书库存类，该类有三个数据成员:name, publisher, price, count，分别表示该图书的书名（字符串型）、出版社（字符串型）、单价（小数类型）、库存数量（整数类型）,通过构造函数传值进行初始化。图书的初始信息存储在books.txt文件中，每行表示一种图书，每行有四列分别表示产品的四个信息。要求从文件读取所有书籍信息，保存在列表中，按出版社和库存量排序，保存到文件。

class Book:
def __init__(self, name, publisher, price, count):
self.name = name
self.publisher = publisher
self.price = price
self.count = count

def load_books(file_name):
books = []
with open(file_name, 'r') as f:
for line in f:
name, publisher, price, count = line.strip().split(',')
book = Book(name, publisher, float(price), int(count))
books.append(book)
return books

def save_books(file_name, books):
with open(file_name, 'w') as f:
for book in books:
f.write('{},{},{},{}\n'.format(book.name, book.publisher, book.price, book.count))

def sort_by_publisher_and_count(books):
return sorted(books, key=lambda x: (x.publisher, -x.count))

books = load_books('books.txt')
sorted_books = sort_by_publisher_and_count(books)
save_books('sorted_books.txt', sorted_books)