Can lambda be used instead of a method, as a key in sorted()?

Question

This is my first time asking a question. I've already got so much help from you without even asking. (Gratitude face). So, I found this useful piece of code from around here a few weeks ago.

import re

def yearly_sort(value):
    numbers = re.compile(r'(\d+)')
    parts = numbers.split(value)
    parts[1::2] = map(int, parts[1::2])
    return parts

It works perfectly here:

def get_files_sorted(path_to_dir):
   file_names = []
   for root, dirs, files in os.walk(path_to_dir):
      for file_name in sorted(files, key=yearly_sort):
         file_names.append(os.path.join(root, file_name))
   return file_names

Now, I'm facing a problem describing the above function (as you can already see from a non-descriptive method name).

What should be the name of above method (instead of some_sort())?

Can this method be squeezed somehow in a lambda such that key in the sorted() can bind to key=lambda?

Why do you feel the need to replace it with a lambda? Do you understand how `lambda` works? — Ignacio Vazquez-Abrams, Sep 22 '16 at 11:34
Can you write function yearly_sort as lambda function, then yes — AlokThakur, Sep 22 '16 at 11:39
@IgnacioVazquez-Abrams In my opinion its not suitable for a method. My team is really strict about _descriptive naming_ and I am unable to describe it properly. Yes I do understand how lambda works but, do not know enough for this one. — Umair Ahmad, Sep 22 '16 at 11:44
When coding guidelines induce programmers to jump through hoops (and make the code more cryptic) to evade adding a simple function... — greggo, Sep 22 '16 at 12:45

score 2 · Answer 1 · edited May 23 '17 at 12:15

2

It definitely can be lambda function. For example look at that question.

But if you have complex function you should never move it to lambda because readability significantly decreases.

So here is Zen of Python

Complex is better than complicated.

edited May 23 '17 at 12:15

Community

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answered Sep 22 '16 at 11:38

vishes_shell

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score 0 · Accepted Answer · answered Sep 22 '16 at 11:40

0

you could squeeze it into a lambda provided that numbers is previously compiled (which increases performance)

numbers = re.compile(r'(\d+)')
for file_name in sorted(files, key=lambda value : [int(x) if x.isdigit() else 0 for x in numbers.split(value)][1::2]):

In that case, we do an unnecessary test for items #0 and #3 onwards. Maybe it could be better, but that's the risk with complex lambdas: performance & lisibility can suffer.

answered Sep 22 '16 at 11:40

Jean-François Fabre

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for file_name in sorted(files, key=lambda name: [ int(numbers.split(name)[1]) ]): Can this be used instead? – Umair Ahmad Sep 23 '16 at 06:54
if it does the same (you never provided any input string), then yes! – Jean-François Fabre Sep 23 '16 at 07:34
Input string is like `"asdf_1234_asdf1234asdf.txt"` yes it works a lot better now. Thanks :) @Jean – Umair Ahmad Sep 26 '16 at 07:37

Can lambda be used instead of a method, as a key in sorted()?

2 Answers2