Convert sort from Python2 to Python3

Question

I've written a sort in Python2, I'm trying to convert it into Python3 which asks for a key and says no more cmp function is available :

test.sort(lambda x, y: cmp(x[2],y[2]) or cmp(x[4], y[4]) or cmp(y[9], x[9]))

Any advices ?

Best regards,

At which point exactly are you stuck? Please edit your question accordingly refering to How do I ask a good question — Tom M
– Tom M, Commented Sep 18, 2018 at 11:20
Purely out of curiosity - what's that sort supposed to do? You're always going to end up with whatever the last comparison of elements 2, 4 or 9 aren't equal (either -1 or 1) or just 0 for equal... at the end... that seems almost randomly sorting to me. I have a feeling that's not a sort you wanted even if you could use it... are you sure what you're after as a key isn't just key=lambda L: (L[2], L[4], L[9]) so you get some sort of "order" there? — Jon Clements
– Jon Clements, Commented Sep 18, 2018 at 11:24
There are two separate problems here: 1) Finding a replacement for the cmp function, and 2) Making the sort work with a key= function. Those two separate problems have two separate answers, so in the future please ask about each problem individually. — Aran-Fey
– Aran-Fey, Commented Sep 18, 2018 at 11:35
What's the structure of test? Eg, is it a list of lists, or a list of tuples? — PM 2Ring
– PM 2Ring, Commented Sep 18, 2018 at 11:35
test is created into a loop like that : test.append((id, sexe, nom, prenom, date_naissance, telephone, sejour_id, etat, type, valeur)) — Vince
– Vince, Commented Sep 18, 2018 at 12:22

blue note · Accepted Answer · 2018-09-18 14:34:28Z

5

The official python 3 documentation explains in this section the proper way of converting this from python 2 to 3.

The original cmp function simply does something like

def cmp(x, y):
   if x == y:
       return 0
   elif x > y:
       return 1
   else:
       return -1

That is, it's equivalent to sign(x-y), but also supports strings and other data types.

However, your problem is that the current function of sort doesn't work with a comparison function with two arguments, but with a single key function of one argument. Python provides functools.cmp_to_key to help you convert it, so, do something like

test.sort(key = functools.cmp_to_key(
    lambda x, y: cmp(x[2],y[2]) or cmp(x[4], y[4]) or cmp(y[9], x[9])
))

edited Sep 18, 2018 at 14:34

answered Sep 18, 2018 at 11:14

blue note

29.5k10 gold badges83 silver badges110 bronze badges

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

Collectives™ on Stack Overflow

Convert sort from Python2 to Python3

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related