Can not break out of Python “while True” loop

Question

book1 = {"Name":"Biology","id":"001","Author":['Alice', 'Bob'],"Copies":5,"Owners":2}
book2 = {"Name":"Chemistry","id":"002","Author":['Alice'],"Copies":3,"Owners":1}
books = [book1,book2]

def adminMenu():
    print("Welcome Admin! What do you want to do?")
    print("1-List Books")
    print("2-Create a book")
    print("3-Clean a book")
    print("4-Search for a book")
    print("5-Change number of copies of book by id")
    print("6-Show students borrowed a book by id")
    print("7-List Users by id")
    print("8-Create User")
    print("9-Delete User")
    print("10-Exit")
    yourChoice = int(input("Your choice: "))
    if yourChoice == 2:
        while True:
            id = input("What is the id you want to give for the book?: ")
            for book in books:
                if id == book["id"]:
                   print("This id is already in use!")
                else:
                    break

Hello I'm trying to create a simple library management system using python 3.8.3. I try to code the create a book section and if the book id already exist, the program should ask for the id again but it doesn't seems to work. What's the mistake that I do here?

    while True:
        id = input("What is the id you want to give for the book?: ")
        for book in books:
            if id == book["id"]:
               print("This id is already in use!")
            else:
                break

Answer 1

Create a list of ids and then check if the input id exists in the list:

book1 = {"Name":"Biology","id":"001","Author":['Alice', 'Bob'],"Copies":5,"Owners":2}
book2 = {"Name":"Chemistry","id":"002","Author":['Alice'],"Copies":3,"Owners":1}
books = [book1,book2]

book_ids = []
for book in books:
        book_ids.append(book.get("id", None))    
# print(book_ids)
def adminMenu():
    print("Welcome Admin! What do you want to do?")
    print("1-List Books")
    print("2-Create a book")
    print("3-Clean a book")
    print("4-Search for a book")
    print("5-Change number of copies of book by id")
    print("6-Show students borrowed a book by id")
    print("7-List Users by id")
    print("8-Create User")
    print("9-Delete User")
    print("10-Exit")
    yourChoice = int(input("Your choice: "))
    if yourChoice == 2:
        while True:
            b_id = input("What is the id you want to give for the book?: ")
            if b_id in book_ids:
               print("This id is already in use! Please Try Again")
            else:
                # Create the book here
                print("Creating book ...")
                break

adminMenu()

OUTPUT:

Welcome Admin! What do you want to do?                                                                                                                                       
1-List Books                                                                                                                                                                 
2-Create a book                                                                                                                                                              
3-Clean a book                                                                                                                                                               
4-Search for a book                                                                                                                                                          
5-Change number of copies of book by id 
6-Show students borrowed a book by id                                                                                                                                        
7-List Users by id                                                                                                                                                           
8-Create User                                                                                                                                                                
9-Delete User                                                                                                                                                                
10-Exit                                                                                                                                                                      
Your choice: 2                                                                                                                                                               
What is the id you want to give for the book?: 001                                                                                                                           
This id is already in use! Please Try Again                                                                                                                                  
What is the id you want to give for the book?: 002
This id is already in use! Please Try Again                                                                                                                                  
What is the id you want to give for the book?: 003
Creating book ...

Answer 2

This is from one of my first projects:

def get_valid_answer():
    while True:
        answer = input("Type [A] or [B] to continue")
        if answer in "AB":
            return answer
        print("Invalid input, please only type [A] or [B]")

You'd have to change it a bit to work as you're trying to but shouldn't be that hard.

Answer 3

The main error isnʼt Python related but a common coding mistake. Try to perform the cycle in mind and check what is done if you enter 002; it will compare with "Biology", find that ids are different and break without comparing to second book ("Chemistry" with id "002")... is this what you try to reach? I doubt. As this isnʼt a place to teach basics, I stop talking here. Ask your teacher to explain.

For Python specifics, Iʼd deter from using id as variable name because it concurs with standard Python function.

Answer 4

You're doing a break on your else which is causing it to leave your for-loop :

while True:
    bookId = input("What is the id you want to give for the book?: ")
    for book in books:
        # Check if the id already exists, otherwise continue with checking the existing books
        if bookId == book["id"]:
            print("This id is already in use!")
            break # Break to leave the loop

PS Also used bookId instead of id as it can be confusing to just use id when your code base gets larger.

Answer 5

Following this logic, without using while True (Is a bad practice )

book_exists = True

while book_exists == True:
    id = input("What is the id you want to give for the book?: ")

    for book in books:

        if id == book["id"]:
            book_exists = True
            break
        else:
            book_exists = False
        print("book exists = %s" % book_exists)