Question

I am a very new in Python so please forgive me the basic question.

I have an array with 400 float elements, and I need to add the first term with the second and divide by two.

I was trying something like:

x1=[0,...,399]

n = len(x1)

x2 = []

i = 0
for i in range(0,n): 
    x2[i]=(x1[i]+x1[i+1])/2

But it gives me the error: IndexError: list assignment index out of range

Thank you in advance.

Answer 1

The problem here is that you cannot assign a value to an index in a list that is higher than the length of the list. Since you just want to keep adding items to the list, use the list.append() method instead:

n = len(x1)

x2 = []

i = 0
for i in range(n-1): 
    x2.append((x1[i]+x1[i+1])/2)

Note that I also decreased the range by one, otherwise x1[i+1] will cause an IndexError.