Reversing a List Recursively: The Brackets That Make It Legal

Why must L[0] be wrapped as [L[0]] before concatenating it after my_rev(L[1:]) — and what does that say about the type every return must hand back?

Finger exercises

Short drills on what this video just taught. Write the code, run the checks, and reveal the answer only if you are stuck.

0 / 5 passed

Exercise 1 of 5

Make the concatenation legal

Someone has already reversed the remainder of a list for you. You are handed these two names:

items = [3, 8, 12, 5, 9]
rest_reversed = [9, 5, 12, 8]

Using both of them, finish the job: assign to combined the full reversal of items, built by putting the element that was peeled off items where it belongs relative to rest_reversed.

Concatenation joins a list to a list. (Hint: items[0] peels the first element, + concatenates, and square brackets build a list.)

# Exercise 1: the remainder is already reversed — place the peeled element to finish it.
items = [3, 8, 12, 5, 9]
rest_reversed = [9, 5, 12, 8]

combined = ...  # your code here

# Exercise 1: the remainder is already reversed — place the peeled element to finish it.
items = [3, 8, 12, 5, 9]
rest_reversed = [9, 5, 12, 8]

combined = ...  # your code here

Python runs in your browser

⌘/Ctrl + Enter runs

is a list

is one flat list, with every element of the original in it

puts the peeled element at the right end

matches the full reversal of the original list

←Previous Nested Lists: Flatten, Search, and Why Loops Fall Short Next deep_rev: One Type Test Reverses Every Layer →