编写一个Python程序的图书管理系统源代码

编写一个简单的图书管理系统的Python源代码，我们可以用字典来存储书籍信息，例如书名、作者和库存。这里提供一个基本的例子：

class LibrarySystem:
    def __init__(self):
        self.books = {}  # 使用字典存储书籍信息

    def add_book(self, title, author, quantity):
        if title in self.books:
            print("Book already exists.")
        else:
            self.books[title] = {'author': author, 'quantity': quantity}
            print(f"Book '{title}' added successfully.")

    def remove_book(self, title):
        if title not in self.books:
            print("Book not found.")
        elif self.books[title]['quantity'] == 0:
            print("Book is out of stock.")
        else:
            self.books[title]['quantity'] -= 1
            if self.books[title]['quantity'] > 0:
                print(f"Book '{title}' removed.")
            else:
                del self.books[title]
                print(f"Book '{title}' has been returned to inventory.")

    def borrow_book(self, title):
        if title not in self.books or self.books[title]['quantity'] == 0:
            print("Book unavailable.")
        else:
            self.books[title]['quantity'] -= 1
            print(f"You borrowed '{title}'. It now has {self.books[title]['quantity']} copies left.")

    def return_book(self, title):
        if title in self.books and self.books[title]['quantity'] < 0:
            print("Book was already returned.")
        else:
            self.books[title]['quantity'] += 1
            print(f"{title} returned. Now available for borrowing.")


# 示例用法
library = LibrarySystem()
library.add_book("Harry Potter", "J.K. Rowling", 3)
library.borrow_book("Harry Potter")
library.return_book("Harry Potter")

这个系统允许添加新书、移除已借出的书、查看库存并借还书。然而，这只是一个非常简化的模型，实际应用可能需要数据库支持，错误处理和用户界面。