list index out of bounds for not the obvious reason numpy

Question

I'm not sure why but I keep getting this error, even though the list index does not exceed the number of indexes. The code getting this error is below:

    normalisedFaces = np.array([])
    for f in range(len(vertextNormalIndices)):
        nF1 = vecNormals[vertextNormalIndices[f][0][0]]
        nF2 = vecNormals[vertextNormalIndices[f][1][0]]
        nF3 = vecNormals[vertextNormalIndices[f][2][0]]
        normalisedFaces = np.hstack((normalisedFaces,(np.add(nF1,np.add(nF2,nF3))/ 3)))
        print(f)
    time.sleep(3)
    print(normalisedFaces[f])

My only guess is that I'm reaching the end of the max size of an array(?) For this example, the loop has the range of 529 , but the error comes up when I reach 519. If I change the loop to something like:

    for f in range(len(vertextNormalIndices)-200):

Then it reaches the end of the range (so, in this case: 329).

How would one go about fixing this? If possible, I'd prefer not to have to nest this loop and have to split-up the size of each array to eg %max==300

Any guidance would be greatly appreciated

I've attached a screenshot of the error here:

The last 8 indexes of vertexNormalIndices: (So, gets the first number of each row eg 278, 195, 281)

Answer 1

Per your comments, and looking at your traceback, the error is in this line:
nF1 = vecNormals[vertextNormalIndices[f][0][0]]

So, the error must be that either vertextNormalIndices[519] or vertextNormalIndices[519][0] is an empty list - try printing them out in the loop.

As an aside:

The 'Pythonic' way to iterate through a list is to do it directly, and if you also need to get the index of each element, you should use enumerate :

normalisedFaces = np.array([])
for f, vertexNormalIndex in enumerate(vertextNormalIndices):
    nF1 = vecNormals[vertextNormalIndex[0][0]]
    nF2 = vecNormals[vertextNormalIndex[1][0]]
    nF3 = vecNormals[vertextNormalIndex[2][0]]
    normalisedFaces = np.hstack((normalisedFaces,(np.add(nF1,np.add(nF2,nF3))/ 3)))
    print(f)
time.sleep(3)
print(normalisedFaces[f])