reversed()

reversed(seq)

Returns: reverse iterator · Updated March 13, 2026 · Built-in Functions

built-in iteration sequence reverse

The reversed() function takes a sequence or object supporting __reversed__ and returns a reverse iterator. It works on lists, tuples, strings, ranges, and any custom object that implements __reversed__ or both __len__ and __getitem__. Unlike slicing with [::-1], reversed() returns a lazy iterator that generates elements on demand, which is more memory-efficient for large sequences.

Syntax

reversed(seq)

Parameters

Parameter	Type	Default	Description
`seq`	sequence or iterable	—	A sequence (list, tuple, string, range) or any object with `__reversed__` method

Returns: A reverse iterator that yields elements from the sequence in reverse order. Convert to a list or tuple to materialize all values.

Examples

Basic usage with a list

The most common use case is reversing a list:

numbers = [1, 2, 3, 4, 5]
for num in reversed(numbers):
    print(num)
# 5
# 4
# 3
# 2
# 1

Reversing a string

Strings are sequences, so reversed() works on them too:

text = "hello"
reversed_text = ''.join(reversed(text))
print(reversed_text)
# olleh

Converting to a list

Since reversed() returns an iterator, convert to a list if you need a list:

numbers = [1, 2, 3]
reversed_list = list(reversed(numbers))
print(reversed_list)
# [3, 2, 1]

Using with range

Works with range objects for numeric sequences:

for i in reversed(range(5)):
    print(i)
# 4
# 3
# 2
# 1
# 0

Common Patterns

Processing items in reverse order

When you need to process list items from end to beginning:

tasks = ["wake up", "brush teeth", "eat breakfast", "go to work"]
for task in reversed(tasks):
    print(f"Undoing: {task}")
# Undoing: go to work
# Undoing: eat breakfast
# Undoing: brush teeth
# Undoing: wake up

Building a reversed copy

Create a new list in reverse order without modifying the original:

original = [1, 2, 3, 4, 5]
reversed_copy = list(reversed(original))
print(original)
# [1, 2, 3, 4, 5]
print(reversed_copy)
# [5, 4, 3, 2, 1]

Using with custom objects

Objects implementing __reversed__ work automatically:

class Countdown:
    def __init__(self, start):
        self.start = start
    
    def __iter__(self):
        return iter(range(self.start, 0, -1))
    
    def __reversed__(self):
        return range(1, self.start + 1)

countdown = Countdown(5)
print(list(reversed(countdown)))
# [1, 2, 3, 4, 5]

Comparison with slice reversal

The slice [::-1] also reverses sequences but creates a new list immediately:

numbers = [1, 2, 3]
sliced = numbers[::-1]
print(sliced)
# [3, 2, 1]

# reversed() is more memory-efficient for large sequences
# because it yields items lazily