Having an object array in python, how can I classify its elements by an attribute?

Question

In Python, is there a function that classifies and orders an array of objects by an attribute?

Example:

class Book:
    """A Book class"""
    def __init__(self,name,author,year):
        self.name = name
        self.author = author
        self.year = year

hp1 = Book("Harry Potter and the Philosopher's stone","J.k Rowling",1997)
hp2 = Book("Harry Potter and the chamber of secretse","J.k Rowling",1998)
hp3 = Book("Harry Potter and the Prisioner of Azkaban","J.k Rowling",1999)

#asoiaf stands for A Song of Ice and Fire
asoiaf1 = Book("A Game of Thrones","George R.R Martin",1996)
asoiaf2 = Book("A Clash of Kings","George R.R Martin",1998)

hg1 = Book("The Hunger Games","Suzanne Collins",2008)
hg2 = Book("Catching Fire","Suzanne Collins",2009)
hg3 = Book("Mockingjaye","Suzanne Collins",2010);

books = [hp3,asoiaf1,hp1,hg1,hg2,hp2,asoiaf2,hg3]
#disordered on purpose

organized_by_autor = magic_organize_function(books,"author")

Does the magic_organize_function exist? Otherwise, what would it be?

Answer 1

Sorting by author is one way:

sorted_by_author = sorted(books, key=lambda x: x.author)
for book in sorted_by_author:
    print(book.author)

Output:

George R.R Martin
George R.R Martin
J.k Rowling
J.k Rowling
J.k Rowling
Suzanne Collins
Suzanne Collins
Suzanne Collins

You can also nicely group by author using itertools.groupby:

from itertools import groupby

organized_by_author = groupby(sorted_by_author, key=lambda x: x.author)

for author, book_from_author in organized_by_author:
    print(author)
    for book in book_from_author:
        print('    ', book.name)

Output:

George R.R Martin
     A Game of Thrones
     A Clash of Kings
J.k Rowling
     Harry Potter and the Prisioner of Azkaban
     Harry Potter and the Philosopher's stone
     Harry Potter and the chamber of secretse
Suzanne Collins
     The Hunger Games
     Catching Fire
     Mockingjaye

Note: You need to feed groupby the sorted sorted_by_author.