Python List `sort()` Method

list.sort() is the built-in list method for sorting items in a list.

Use this page as a quick reference for what sort() does, how its main arguments work, and the beginner mistakes to avoid.

Quick example

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

Use list.sort() to sort a list in place. It changes the original list and returns None.

What `list.sort()` does

list.sort():

Sorts the items of a list in place
Changes the original list
Returns None
Works for numbers and strings when items can be compared

This means the list itself is updated after you call the method.

numbers = [5, 2, 9, 1]
numbers.sort()

print(numbers)

Output:

[1, 2, 5, 9]

If you are still learning how lists work, see the Python lists beginner guide.

Basic syntax

my_list.sort(key=None, reverse=False)

Main arguments:

key lets you sort by a custom rule
reverse=True sorts in descending order
If no arguments are given, sorting is ascending

Example:

numbers = [4, 1, 7, 2]
numbers.sort(reverse=True)

print(numbers)

Output:

[7, 4, 2, 1]

Sort numbers

Use sort() when you want to sort numbers in ascending order.

numbers = [10, 3, 8, 1]
numbers.sort()

print(numbers)

Output:

[1, 3, 8, 10]

Use reverse=True for descending order:

numbers = [10, 3, 8, 1]
numbers.sort(reverse=True)

print(numbers)

Output:

[10, 8, 3, 1]

The important thing to remember is that the original list is updated after the method call.

For a task-focused guide, read how to sort a list in Python.

Sort strings

Strings are sorted alphabetically by default.

words = ["banana", "apple", "cherry"]
words.sort()

print(words)

Output:

['apple', 'banana', 'cherry']

Uppercase and lowercase letters affect the result:

words = ["banana", "Apple", "cherry"]
words.sort()

print(words)

Output:

['Apple', 'banana', 'cherry']

If you want case-insensitive sorting, use key=str.lower:

words = ["banana", "Apple", "cherry"]
words.sort(key=str.lower)

print(words)

Output:

['Apple', 'banana', 'cherry']

The original spelling stays the same. Python only uses str.lower as the sorting rule.

Using the `key` argument

The key argument changes how each item is compared.

Common examples:

len to sort by length
str.lower to sort strings without case problems

Sort words by length:

words = ["pear", "banana", "fig", "apple"]
words.sort(key=len)

print(words)

Output:

['fig', 'pear', 'apple', 'banana']

Sort strings without case sensitivity:

words = ["Bob", "alice", "Carol"]
words.sort(key=str.lower)

print(words)

Output:

['alice', 'Bob', 'Carol']

The key argument is especially useful when the default alphabetical or numeric order is not what you want.

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

list.sort() and sorted() both sort data, but they work differently.

list.sort():

Changes the existing list
Returns None

sorted():

Returns a new sorted list
Leaves the original unchanged

Example:

numbers = [3, 1, 2]

new_list = sorted(numbers)

print(numbers)
print(new_list)

Output:

[3, 1, 2]
[1, 2, 3]

Use sorted() when you want to keep the original list unchanged.

You can learn more in Python sorted() explained and sorted() vs list.sort() explained.

Common mistakes

Here are the most common beginner mistakes with list.sort().

Assigning the result of `sort()`

This is a very common mistake:

numbers = [3, 1, 2]
result = numbers.sort()

print(result)
print(numbers)

Output:

None
[1, 2, 3]

sort() does not return the sorted list. It returns None.

If you want a new list, use sorted() instead.

Sorting mixed types

Python cannot always compare different types directly.

items = [1, "two", 3]
items.sort()

This raises a TypeError because Python cannot sort integers and strings together by default.

Forgetting that `sort()` only works on lists

sort() is a list method. It does not work directly on tuples or strings.

Wrong:

text = "python"
text.sort()

Strings do not have a sort() method.

If needed, convert the data first:

letters = list("python")
letters.sort()

print(letters)

Output:

['h', 'n', 'o', 'p', 't', 'y']

Not using `key` when custom sorting is needed

If the default order is not correct for your problem, you may need key.

For example, if you want to sort words by length, plain sort() will not do that:

words = ["banana", "fig", "apple"]
words.sort(key=len)

print(words)

Unexpected string order because of uppercase letters

This often surprises beginners:

words = ["zebra", "Apple", "monkey"]
words.sort()

print(words)

Output:

['Apple', 'monkey', 'zebra']

Use key=str.lower if you want case-insensitive sorting.

Useful debugging checks

If sorting is not working as expected, these quick checks can help:

print(my_list)
print(type(my_list))
print(my_list.sort())
print(sorted(my_list))
print([type(item) for item in my_list])

These checks help you confirm:

What values are in the list
Whether the object is really a list
That sort() returns None
Whether sorted() works better for your case
Whether the list contains mixed data types

If your problem is caused by incompatible values, see a guide for fixing sorting-related TypeError problems.

FAQ

Does `list.sort()` return a new list?

No. It changes the original list and returns None.

What is the difference between `sort()` and `sorted()`?

sort() changes the list itself. sorted() creates and returns a new sorted list.

How do I sort in reverse order?

Use:

my_list.sort(reverse=True)

How do I sort strings without case problems?

Use:

my_list.sort(key=str.lower)

This sorts in a case-insensitive way.

Why do I get a `TypeError` when sorting?

Your list may contain values that Python cannot compare directly, such as strings and integers together.

Python List sort() Method

Python List `sort()` Method