IndexError: list index out of range?

Question

Python

Why does this script throw an IndexError: list index out of range error?

import numpy as np
dummy = [1, 1, 5, 6, 7, 9, 4, 4, 2]
x = 1

for j in range(len(dummy)):
if dummy[j] == dummy[j+ 1]:
dummy[j] = 0

print(dummy)

Answer 1

Hello!
Everything is very simple! When the loop gets to the last number, which is 8, which is the index of the last element, you tell the code to check
dummy[8] == dummy[9]
But there is no element at index 9, so that's the IndexError.
Also, you apparently forgot to make dummy numpy an array, otherwise why import numpy?
And instead of range(len()) it is better to use enumerate

import numpy as np
dummy = np.array([1, 1, 5, 6, 7, 9, 4, 4, 2])
x = 1

for n,j in enumerate(dummy[:-1]):
  if dummy[n] == dummy[n+1]:
    dummy[j] = 0

print(dummy)