`list.sort()` vs `sorted()`

Introduction

Python offers two distinct ways to sort iterables. Choosing the right one in an interview demonstrates your understanding of memory management and mutability.

1. `list.sort()` (In-Place)

The .sort() method belongs strictly to the list class. It sorts the list in place and returns None.

nums = [3, 1, 4, 1, 5]

# Sorts the original list, returns None
result = nums.sort()

print(nums)   # [1, 1, 3, 4, 5]
print(result) # None

When to use `list.sort()`

Use .sort() when you are given a list, you don't need to preserve the original order, and you want to save memory. - Space Complexity: \(O(N)\) (Timsort still requires some extra memory, though it sorts the container in place).

Common Interview Trap

Because .sort() returns None, you cannot chain it or use it in an assignment.

# TypeError: 'NoneType' object is not iterable
# for num in nums.sort():
#     print(num)

# Incorrect assignment
# sorted_nums = nums.sort()

2. `sorted()` (Out-of-Place)

The sorted() function is a built-in function that takes any iterable (lists, strings, tuples, dictionaries) and returns a new sorted list.

nums = [3, 1, 4, 1, 5]

# Creates a brand new list
new_nums = sorted(nums)

print(nums)     # [3, 1, 4, 1, 5] (Unchanged)
print(new_nums) # [1, 1, 3, 4, 5]

Sorting Strings and Tuples

Because strings and tuples are immutable, they do not have a .sort() method. You must use sorted().

s = "cba"
# Returns a list, must join back to string
sorted_str = "".join(sorted(s))

When to use `sorted()`

Use sorted() when you need to sort an immutable iterable, or when the problem requires you to preserve the original array. - Space Complexity: \(O(N)\) to create the new list, plus \(O(N)\) for the Timsort algorithm.

Summary

Use list.sort() to mutate a list in place and save memory. Remember it returns None.
Use sorted(iterable) for strings, tuples, or when you need a new list. It always returns a list.

list.sort() vs sorted()

Introduction

1. list.sort() (In-Place)

When to use list.sort()