[Python] CodeSignal - 'Mutate Array'

The coding question asks:

Given an integer n and an array a of length n, your task is to apply the following mutation to a:

Array a mutates into a new array b of length n. For each i from 0 to n - 1, b = a[i - 1] + a + a[i + 1]. If some element in the sum a[i - 1] + a + a[i + 1] does not exist, it should be set to 0. For example, b[0] should be equal to 0 + a[0] + a1.
​

My Code:

def solution(n, a):
b = [None] * n
for i in range(0, n-1):
print('i = ', i)
if i <= 0:
b = 0 + a + a[i+1]
print('IF 1')
elif i >= n-1:
b = a[i-1] + a + 0
print('IF 2')
else:
b = a[i-1] + a + a[i+1]
print('IF 3')
return b


The issue is that the for loop does not seem to run a sufficient amount of times, and I cannot change the range according to the question. Any ideas? See results below.



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