How to Sort a List in Python: Simple Guide with Examples

To sort a list in Python, use the list.sort() method to sort the list in place or the sorted() function to get a new sorted list. Both allow sorting in ascending order by default and can sort in descending order by setting reverse=True.

Syntax

The two main ways to sort a list in Python are:

• list.sort(key=None, reverse=False): Sorts the list itself and changes its order.
• sorted(iterable, key=None, reverse=False): Returns a new sorted list from any iterable without changing the original.

Parameters:

• key: Optional function to customize sorting criteria.
• reverse: Optional boolean to sort in descending order if True.

python

my_list.sort()
sorted_list = sorted(my_list)

# With options
my_list.sort(reverse=True)
sorted_list = sorted(my_list, key=lambda x: x*2, reverse=True)

Example

This example shows sorting a list of numbers in ascending and descending order using both list.sort() and sorted(). It also shows that sorted() returns a new list while list.sort() changes the original list.

python

numbers = [5, 2, 9, 1, 5, 6]

# Sort in place (ascending)
numbers.sort()
print("Sorted with list.sort():", numbers)

# Sort in place (descending)
numbers.sort(reverse=True)
print("Descending with list.sort():", numbers)

# Original list
numbers = [5, 2, 9, 1, 5, 6]

# Get new sorted list (ascending)
sorted_numbers = sorted(numbers)
print("Sorted with sorted():", sorted_numbers)

# Get new sorted list (descending)
sorted_numbers_desc = sorted(numbers, reverse=True)
print("Descending with sorted():", sorted_numbers_desc)

# Original list remains unchanged
print("Original list after sorted():", numbers)

Output

Sorted with list.sort(): [1, 2, 5, 5, 6, 9]
Descending with list.sort(): [9, 6, 5, 5, 2, 1]
Sorted with sorted(): [1, 2, 5, 5, 6, 9]
Descending with sorted(): [9, 6, 5, 5, 2, 1]
Original list after sorted(): [5, 2, 9, 1, 5, 6]

Common Pitfalls

Common mistakes when sorting lists include:

• Using list.sort() expecting it to return a new list (it returns None).
• Not realizing list.sort() changes the original list.
• Forgetting to use reverse=True to sort in descending order.
• Trying to sort lists with mixed data types that cannot be compared.

python

my_list = [3, 1, 2]

# Wrong: expecting a new sorted list
sorted_list = my_list.sort()
print(sorted_list)  # Prints None

# Right: use sorted() to get new list
sorted_list = sorted(my_list)
print(sorted_list)  # Prints [1, 2, 3]

Output

None
[1, 2, 3]

Quick Reference

Method	Description	Modifies Original?	Returns
list.sort()	Sorts the list in place	Yes	None
sorted(iterable)	Returns a new sorted list	No	New sorted list

Key Takeaways

Use list.sort() to sort a list in place without creating a new list.

Use sorted() to get a new sorted list and keep the original unchanged.

Set reverse=True to sort in descending order.

list.sort() returns None, so don’t assign its result to a variable.

Sorting works best when all list items are comparable.