How to Sort a List in Python

Overview

Python gives you two ways to sort a list. list.sort() sorts the list in place and returns None. sorted() leaves the original untouched and returns a new sorted list. Both accept the same two keyword arguments — key and reverse — so once you know one, you know the other.

Steps

1. Sort in place with list.sort()

nums = [3, 1, 2]
nums.sort()
print(nums)  # [1, 2, 3]

2. Get a new sorted list with sorted()

Use sorted() when you need to keep the original list. It works on any iterable and always returns a list.

src = [3, 1, 2]
result = sorted(src)
print(result)  # [1, 2, 3]
print(src)     # [3, 1, 2] — unchanged

3. Descending order with reverse=True

print(sorted([3, 1, 2], reverse=True))  # [3, 2, 1]

4. Custom order with key=

key takes a function applied to each element to decide the sort order. Sort by length, or case-insensitively with str.lower:

print(sorted(["bb", "a", "ccc"], key=len))          # ['a', 'bb', 'ccc']

words = ["banana", "apple", "Cherry"]
print(sorted(words))                # ['Cherry', 'apple', 'banana']  (uppercase first)
print(sorted(words, key=str.lower)) # ['apple', 'banana', 'Cherry']  (case-insensitive)

5. Sort a list of dictionaries

people = [
    {"name": "Ada", "age": 36},
    {"name": "Bo", "age": 22},
]

by_age = sorted(people, key=lambda p: p["age"])
print([p["name"] for p in by_age])  # ['Bo', 'Ada']

Runnable example

A complete, runnable example — open it in the Python compiler:

products = [
    {"name": "Pen", "price": 3},
    {"name": "Notebook", "price": 6},
    {"name": "Eraser", "price": 1},
]

# Cheapest first, without changing the original list
cheapest_first = sorted(products, key=lambda p: p["price"])
for p in cheapest_first:
    print(p["name"], p["price"])
# Eraser 1
# Pen 3
# Notebook 6

Common pitfalls

Like JavaScript, Python's sort is stable: elements that compare equal keep their original order, so you can sort by one key and then another to get a multi-level sort.

Frequently asked questions

What's the difference between sort() and sorted() in Python?

list.sort() sorts the list in place and returns None. sorted() returns a new sorted list and leaves the original unchanged. Both accept key and reverse.

Why does my list become None after sorting?

You assigned the result of list.sort(), which returns None. Call .sort() as a statement (nums.sort()), or use sorted(nums) if you want the sorted list as a value.

How do I sort a list of dictionaries by a key?

Pass a key function that returns the field to sort on: sorted(items, key=lambda d: d['age']). Add reverse=True for descending order.

How do I sort strings case-insensitively?

Use key=str.lower, e.g. sorted(words, key=str.lower). The default sort is case-sensitive and orders uppercase letters before lowercase ones.