Reverse a list in Python ([::-1], reverse(), reversed())

Python has three ways to reverse a list. The difference is whether you get a new list or change the original one.

The program

python

numbers = [1, 2, 3, 4, 5]

backwards = numbers[::-1]
print("Reversed copy:", backwards)
print("Original:     ", numbers)

numbers.reverse()
print("After reverse():", numbers)

output

Reversed copy: [5, 4, 3, 2, 1]
Original:      [1, 2, 3, 4, 5]
After reverse(): [5, 4, 3, 2, 1]

How it works

numbers[::-1] is a slice with a step of -1. It walks the list from the end to the start and builds a new list. The original list does not change.
numbers.reverse() changes the list itself (in place) and returns None. So print(numbers.reverse()) prints None, which surprises many beginners.

Looping backwards

When you only want to loop over the items from last to first, reversed() does that without making a copy of the list:

python

for name in reversed(["Ada", "Grace", "Hedy"]):
    print(name)

output

Hedy
Grace
Ada

reversed() gives an iterator, not a list. Wrap it in list(...) if you need a list: list(reversed(numbers)).