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Sort Lists

Sorting lists is a common task in Python when you need to organize data in a specific order. Python provides powerful and flexible ways to sort lists in-place or by creating a new sorted list.

Sort a List Using sort()

The sort() method sorts the list in ascending order by default and modifies the original list.
python
numbers = [3, 1, 4, 2]
numbers.sort()
print(numbers)
python
fruits = ["banana", "apple", "cherry"]
fruits.sort()
print(fruits)

Sort in Descending Order

Use the reverse=True argument.
python
numbers = [3, 1, 4, 2]
numbers.sort(reverse=True)
print(numbers)
python
fruits = ["banana", "apple", "cherry"]
fruits.sort(reverse=True)
print(fruits)

Sort a List Using sorted()

The sorted() function returns a new sorted list without changing the original.
python
numbers = [5, 2, 9, 1]
new_list = sorted(numbers)
print(new_list)
print(numbers)
python
words = ["cat", "elephant", "dog"]
print(sorted(words))

Sort by Length Using key

The key parameter allows custom sorting logic.
python
words = ["apple", "banana", "kiwi"]
words.sort(key=len)
print(words)
python
numbers = ["10", "2", "30"]
numbers.sort(key=int)
print(numbers)

Sort List of Tuples

python
data = [(1, 3), (4, 1), (2, 2)]
data.sort()
print(data)
python
data.sort(key=lambda x: x[1])
print(data)

Sort with Case Sensitivity

By default, uppercase letters come first.
python
names = ["apple", "Banana", "cherry"]
names.sort()
print(names)

Case-Insensitive Sort

python
names.sort(key=str.lower)
print(names)

Reverse a List Without Sorting

python
numbers = [1, 2, 3]
numbers.reverse()
print(numbers)

Sort Numeric vs String Values

python
values = ["100", "20", "3"]
values.sort()
print(values)
python
values.sort(key=int)
print(values)

Sorting Nested Lists

python
matrix = [[3, 1], [1, 5], [2, 2]]
matrix.sort()
print(matrix)
python
matrix.sort(key=lambda x: x[1])
print(matrix)

Common Mistakes

Expecting sort() to Return a List

python
numbers = [3, 2, 1]
result = numbers.sort()
print(result)
sort() returns None.

Mixing Incompatible Types

python
# numbers = [1, "2", 3]
# numbers.sort()   # TypeError

Performance Note

  • sort() is faster for large lists
  • sorted() is useful when original order must be preserved
  • Python uses Timsort, which is efficient and stable

Summary

  • sort() modifies the original list
  • sorted() returns a new list
  • reverse=True sorts descending
  • key allows custom sorting logic
  • Sorting is case-sensitive by default
  • Avoid mixing incompatible types