Source: 📖 Python Cookbook ch1.14 p23
When wanting to sort a sequence of objects by a particular attribute, or when wanting to sort a sequence of objects without native comparison, a key argument can be provided to the sorted or sort functions.
class User:
def __init__(self, fname, lname, dob):
self.fname = fname
self.lname = lname
self.dob = dob
juan = User('Juan', 'Coquet', '1995-12-01')
claudio = User('Claudio', 'Coquet', '1953-09-13')
hristo = User('Hristo', 'Zaykov', '1996-04-07')
users = [juan, claudio, hristo]
by_full_name = sorted(users, key=lambda u: (u.lname, u.fname))
# [claudio, juan, hristo]
In the above block of code, a lambda which returns a tuple containing the user's last name and the user's first name to use as the sorting criteria.