how does lambda pick values to return

Question

In a tutorial, I see a piece of code that I verified works: https://wiki.python.org/moin/HowTo/Sorting

>>> student_tuples = [
        ('john', 'A', 15),
        ('jane', 'B', 12),
        ('dave', 'B', 10),
]
>>> sorted(student_tuples, key=lambda student: student[2])   # sort by age
[('dave', 'B', 10), ('jane', 'B', 12), ('john', 'A', 15)]

Why is the student[2] known by python to refer to the third element of each tuple? Why didn't it try to sort by the third tuple, instead of the third item of each tuple?

because it iterates over the iterable passing each subelement, on a side note operator.itemgetter(2) would be more efficeint — Padraic Cunningham
– Padraic Cunningham, Commented Jul 7, 2015 at 13:10
yes itemgetter is done at the c level, a lambda is more expensive, it depends on what you want to do as there are some things you can do with a lambda that itemgetter cannot do but for your example itemgetter would be more efficeint — Padraic Cunningham
– Padraic Cunningham, Commented Jul 7, 2015 at 13:38

Kasravnd · Accepted Answer · 2015-07-07 13:11:54Z

2

Because sorted function sends the elements of its iterable argument to lambda function.and in this case the tuples will be sent to lambda.

key specifies a function of one argument that is used to extract a comparison key from each list element: key=str.lower. The default value is None (compare the elements directly).

edited Jul 7, 2015 at 13:11

answered Jul 7, 2015 at 13:10

Kasravnd

108k19 gold badges167 silver badges195 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

codyc4321 Over a year ago

so that's why key has to take a function

Kasravnd Over a year ago

@codyc4321 Indeed, you want to sort the elements not the list ;)

Collectives™ on Stack Overflow

how does lambda pick values to return

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related