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Jerry Yu
Jerry Yu

Reputation: 11

Python list assignment error but printing the correct result

I'm doing this question on leetcode, why am I printing the correct result, but not getting the correct answer in leetcode? It seems if I do

nums[:]=list(endArray+frontArray)

Then it would work. I think it's some list assignment issue? enter image description here

Upvotes: 0

Views: 151

Answers (1)

Silvio Mayolo
Silvio Mayolo

Reputation: 70267

You've just discovered the difference between variables and their values. A variable in Python always points to a value. It references one but doesn't contain it.

nums = list(endArray+frontArray)

This snippet makes a new, unrelated list and assigns that list to nums. The old list is still out there in memory somewhere unmodified. You just made a new one and assigned it to a local variable that's about to get deleted anyway.

nums[:] = list(endArray+frontArray)

This is an assignment to all positions ([:]) of the current line. We're not making a new list; we're overwriting all of the values in the existing list. Anybody who held a reference to the previous list will see the changes in this case.

Upvotes: 1

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