What Is the Difference Between `Sorted(List)` vs `List. Sort()`?

Maya Lin-Takahashi
Maya Lin-Takahashi
• • 7 min read

List. Sort() Sorts the List and Replaces the Original List, Whereas Sorted(List) Returns a Sorted Copy of the List, Without Changing the Original List. When Is...

What Is the Difference Between `Sorted(List)` vs `List. Sort()`?

list.sort() sorts the list and replaces the original list, whereas sorted(list) returns a sorted copy of the list, without changing the original list.

  • When is one preferred over the other?
  • Which is more efficient? By how much?
  • Can a list be reverted to the unsorted state after list.sort() has been performed?
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6 Answers

sorted() returns a new sorted list, leaving the original list unaffected. list.sort() sorts the list in-place, mutating the list indices, and returns None (like all in-place operations).

sorted() works on any iterable, not just lists. Strings, tuples, dictionaries (you'll get the keys), generators, etc., returning a list containing all elements, sorted.

  • Use list.sort() when you want to mutate the list, sorted() when you want a new sorted object back. Use sorted() when you want to sort something that is an iterable, not a list yet.

  • For lists, list.sort() is faster than sorted() because it doesn't have to create a copy. For any other iterable, you have no choice.

  • No, you cannot retrieve the original positions. Once you called list.sort() the original order is gone.

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What is the difference between sorted(list) vs list.sort()?

  • list.sort mutates the list in-place & returns None
  • sorted takes any iterable & returns a new list, sorted.

sorted is equivalent to this Python implementation, but the CPython builtin function should run measurably faster as it is written in C:

def sorted(iterable, key=None):
    new_list = list(iterable)    # make a new list
    new_list.sort(key=key)       # sort it
    return new_list              # return it

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when to use which?

  • Use list.sort when you do not wish to retain the original sort order (Thus you will be able to reuse the list in-place in memory.) and when you are the sole owner of the list (if the list is shared by other code and you mutate it, you could introduce bugs where that list is used.)
  • Use sorted when you want to retain the original sort order or when you wish to create a new list that only your local code owns.
Maya Lin-Takahashi

Maya Lin-Takahashi

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Maya is a hardware enthusiast who tests and reviews smart home devices, smartphones, wearables, and audio gear. She focuses on practical consumer value and build quality.