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Python Python Collections (2016, retired 2019) Slices Back and Forth

Posted by Marco Koopman
Marco Koopman
5,290 Points

Why does sorted_things.sort() acts differently when you add [:] behind it

favorite_things = ['raindrops on roses', 'whiskers on kittens', 'bright copper kettles', 'warm woolen mittens', 'bright paper packages tied up with string', 'cream colored ponies', 'crisp apple strudels']

sorted_things = favorite_things[:]

sorted_things.sort()

slice1 = favorite_things[1:4] slice2 = favorite_things[5:]

print(sorted_things) print(favorite_things)

Acts like it should but when I change:

sorted_things = favorite_things[:] to sorted_things = favorite_things

It changes favorite things too when I sort sorted_things.

Is this supposed to happen? And why does this happen?

slices.py 
favorite_things = ['raindrops on roses', 'whiskers on kittens', 'bright copper kettles',
                   'warm woolen mittens', 'bright paper packages tied up with string',
                   'cream colored ponies', 'crisp apple strudels']

slice1 = favorite_things[1:4]
slice2 = favorite_things[5:]

sorted_things = favorite_things

sorted_things.sort()

2 Answers

Alexander Davison
Alexander Davison
65,469 Points
Alexander Davison
Alexander Davison
65,469 Points

.sort() is designed to sort the list in place. Therefore, if you call .sort() on a list, it modified the list. Sometimes you don't want to sort it in-place so therefore you use the sorted function.

>>> my_list = [2, 1, 3]
>>> my_list
[2, 1, 3]
>>> sorted(my_list)
[1, 2, 3]
>>> my_list
[2, 1, 3]
>>> my_list.sort()
>>> my_list
[1, 2, 3]
Marco Koopman
Marco Koopman
5,290 Points

Hey, Thanks for the aswer but this is not what I meant.

I was wondering why .sort() effects both favorite_things as sorted_things when I only sort sorted_things.

But when I write the variable value like this: favorite_things[:] It only changes sorted_things.

.sort() shouldn't have any effect on favorite_things because I never use this function on this variable.

Kai Page
Kai Page
4,406 Points
Kai Page
Kai Page
4,406 Points

I'm having this exact same issue. Do we know why?