Changing values of a list of namedtuples

Question

I have a list of namedtuples named Books and am trying to increase the price field by 20% which does change the value of Books. I tried to do:

from collections import namedtuple Book = namedtuple('Book', 'author title genre year price instock') BSI = [        Book('Suzane Collins','The Hunger Games', 'Fiction', 2008, 6.96, 20),        Book('J.K. Rowling', "Harry Potter and the Sorcerer's Stone", 'Fantasy', 1997, 4.78, 12)] for item in BSI:     item = item.price*1.10 print(item.price) 

But I keep getting :

 Traceback (most recent call last):  print(item.price)  AttributeError: 'float' object has no attribute 'price' 

I understand that I cannot set the fields in a namedtuple. How do I go about updating price?

I tried to make it into a function:

def restaurant_change_price(rest, newprice):     rest.price = rest._replace(price = rest.price + newprice)     return rest.price  print(restaurant_change_price(Restaurant("Taillevent", "French", "343-3434", "Escargots", 24.50), 25)) 

but I get an error with replace saying:

 rest.price = rest._replace(price = rest.price + newprice)  AttributeError: can't set attribute 

Can someone let me know why this is happening?

Answer 1

In Python >= 3.7 you can use dataclass decorator with the new variable annotations feature to produce mutable record types:

from dataclasses import dataclass   @dataclass class Book:     author: str     title: str     genre: str     year: int     price: float     instock: int   BSI = [     Book("Suzane Collins", "The Hunger Games", "Fiction", 2008, 6.96, 20),     Book(         "J.K. Rowling",         "Harry Potter and the Sorcerer's Stone",         "Fantasy",         1997,         4.78,         12,     ), ]  for item in BSI:     item.price *= 1.10     print(f"New price for '{item.title}' book is {item.price:,.2f}") 

Output:

New price for 'The Hunger Games' book is 7.66 New price for 'Harry Potter and the Sorcerer's Stone' book is 5.26 

Answer 2

Named tuples are immutable, so you cannot manipulate them.

Right way of doing it:

If you want something mutable, you can use recordtype.

from recordtype import recordtype  Book = recordtype('Book', 'author title genre year price instock') books = [    Book('Suzane Collins','The Hunger Games', 'Fiction', 2008, 6.96, 20),    Book('J.K. Rowling', "Harry Potter and the Sorcerer's Stone", 'Fantasy', 1997, 4.78, 12)]  for book in books:     book.price *= 1.1     print(book.price) 

PS: You may need to pip install recordtype if you don't have it installed.

Bad way of doing it:

You may also keep using namedtuple with using the _replace() method.

from collections import namedtuple  Book = namedtuple('Book', 'author title genre year price instock') books = [    Book('Suzane Collins','The Hunger Games', 'Fiction', 2008, 6.96, 20),    Book('J.K. Rowling', "Harry Potter and the Sorcerer's Stone", 'Fantasy', 1997, 4.78, 12)]  for i in range(len(books)):     books[i] = books[i]._replace(price = books[i].price*1.1)     print(books[i].price)