How do I reverse a list or loop over it backwards?

python

list-reversal

memory-management

performance

byNikita Barsukov·Aug 5, 2024

Flip your list like a pancake with a [::-1] slice or march it backwards using reversed().

# Cooking up a reversed list
flipped_list = [1, 2, 3, 4, 5][::-1]  # Gordon Ramsay would be proud!

# Taking a backward stroll
for item in reversed([1, 2, 3, 4, 5]):  # This item is a rebel, it ignores the norms!
    print(item)

Get your reversal tools

Slice for the win

Checkmate problems, slice your way out! Python's [::-1] slice is the Usain Bolt of list reversal.

Original list objector

Wanna play safe? Use list.reverse() to flip your list in-place. Big lists? No worries, you're covered.

Backward iterator connoisseur

Need to loop over a list in reverse order without any side-effects? reversed() is your friend from memory management land.

Is efficiency your jam?

Packing power with Python 3.11

Python 3.11 onward, list reversal is faster than your car's 0-60! Use timeit to compare performances, especially for mega lists.

Memory or speed? You choose

reversed() or list.reverse(), [::-1] slice or manual reversal, Python gives you the power to choose. Just be careful about list size and memory usage!

It's reversed, now what?

Dabble in elegance with chaining

Combine slicing with other operations and Python lists will look like an elegant ballet performance.

Save the original, create a copy

Always ponder whether you want to alter the original list. To keep it safe, use non-destructive methods like reversed() or slicing [::-1].

Slice, the Python's katana

Go beyond list reversal! Slice notation is a magic spell in Python, master it from the docs!

Manage potential pitfalls

Be careful while modifying

list.reverse() modifies the list in-place. If you don't want to spoil the original list, opt for reversed() or slicing [::-1].

Loops can be tricky

Don't try to be a hero by manually reversing your list. Built-in functions are not only faster but are also debugged by smarter people than us (no offense 😅).