library.py

class Book:
  def __init__(self, title, author):
    self.title = title 
    self.author = author 
    self.is_checked_out = False

  def check_out(self):
    self.is_checked_out = True
    print(f"{self.title} by {self.author} has been checked out.")

  def check_in(self):
    self.is_checked_out = False
    print(f"{self.title} by {self.author} has been checked in.")

class Library:
  def __init__(self):
    self.books = []

  def add_book(self, book):
    self.books.append(book)
    print(f"{book.title} by {book.author} has been added to the library.")

  def check_out_book(self, title): 
    for book in self.books:
      if book.title == title and not book.is_checked_out: 
        book.check_out()
        return
    print(f"Sorry, {title} is not available.")

  def check_in_book(self, title): 
    for book in self.books:
      if book.title == title and book.is_checked_out: 
        book.check_in()
        return
    print(f"Sorry, {title} is not in the library.")

class Client:
  def __init__(self, name):
    self.name = name
    self.checked_out_books = []

  def check_out_book(self, library, title): 
    for book in library.books:
      if book.title == title and not book.is_checked_out: 
        book.check_out()
        self.checked_out_books.append(book)
        return
    print(f"Sorry, {title} is not available.")

  def check_in_book(self, library, title): 
    for book in self.checked_out_books:
      if book.title == title: 
        book.check_in()
        self.checked_out_books.remove(book)
        return
    print(f"Sorry, {title} is not checked out.") 
    

library = Library()
book1 = Book("To Kill a Mockingbird", "Harper Lee") 
library.add_book(book1)

book2 = Book("Pride and Prejudice", "Jane Austen") 
library.add_book(book2)

client1 = Client("John Doe") 
client1.check_out_book(library, "To Kill a Mockingbird") 
client1.check_out_book(library, "Pride and Prejudice")

client2 = Client("Jane Doe") 
client2.check_out_book(library, "To Kill a Mockingbird")

client1.check_in_book(library, "To Kill a Mockingbird")