If you've worked with lists in Python, you've probably come across both sorted() and .sort(). At first glance, they seem to do the same thing — sort data. But behind the scenes, they work quite differently.
Let’s break it down.
✅ sorted() — Returns a New Sorted List
The sorted() in-built function can be used on any iterable: lists, tuples, dictionaries, etc. It doesn’t modify the original object. Instead, it returns a new sorted list.
# syntax:
sorted(iterable, key=None, reverse=False)
nums = [3, 1, 2]
sorted_nums = sorted(nums)
print(sorted_nums) # [1, 2, 3]
print(nums) # [3, 1, 2] — original list is unchanged
You can also sort in reverse or customize sorting with the key argument:
names = ['Alice', 'bob', 'Charlie']
print(sorted(names, key=str.lower)) # ['Alice', 'bob', 'Charlie']
✅ .sort() — Sorts In-Place
The .sort() method is available only for lists. It modifies the list in place and returns None.
# syntax
list.sort(key=None, reverse=False)
nums = [3, 1, 2]
nums.sort()
print(nums) # [1, 2, 3] — original list is changed
Just like sorted(), .sort() also supports key and reverse:
words = ['banana', 'Apple', 'cherry']
words.sort(key=str.lower)
print(words) # ['Apple', 'banana', 'cherry']
⚖️ Key Differences at a Glance
| Feature | sorted() |
.sort() |
|---|---|---|
| Type | Built-in function | List method |
| Return value | New sorted list | None |
| Original list | Unchanged | Modified (in-place) |
| Usable on | Any iterable | Lists only |
Sorting Trivia
Historically, the sorting algorithm used was called Timsort but since Python 3.11 it was replaced by an improved algorithm called Powersort which is based in Timsort.
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