I am trying to debug some old code and need to understand a specific line of code, but it keeps giving errors so I can’t see exactly what is going on. I will simplify it here.

I have two lists: A and B

A = [0,1,2,3]
B = [5,6,7,8]

My question is: Is there any difference between the two snippets of code below?

A[B==0] = 11

or

A[0] = 11

Would initializing list B to 0 while indexing list A be any different than just indexing list A with 0?

>Solution :

To answer your question: A[B==0] and A[0] are in this case equivalent, because B==0 is false.

However, you aren’t initializing list B to 0, you’re comparing it. A[B==0] does not change the value of B. To assign to B in A‘s indexer, you’d need to use the walrus operator, A[B:=0] (which would also be equivalent to A[0]).

Your question implies or invites misunderstanding as it looks to assert that B==0 is initialization/assignment, so I might suggest reviewing the wording of the question for clarity.