Writing Functions That Mutate a List In Place

Why must you loop over `range(len(L))` to change a list in place, and why does such a function return None?

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.

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Exercise 1 of 5

Triple every element in place

You're given the list nums = [4, 7, 1, 9]. Loop over its indices and overwrite each element with three times its value, mutating nums in place rather than building a new list. tripled is already bound to nums, so it will show the result.

nums = [4, 7, 1, 9]
# your code here — loop over the INDICES so you can overwrite each slot
tripled = nums

nums = [4, 7, 1, 9]
# your code here — loop over the INDICES so you can overwrite each slot
tripled = nums

Python runs in your browser

⌘/Ctrl + Enter runs

tripled is a list

every element is three times its old value

changed in place — still the same list object

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