"'generator' object is not subscriptable" error

Question

Why am I getting this error, from line 5 of my code, when attempting to solve Project Euler Problem 11?

for x in matrix:
    p = 0
    for y in x:
        if p < 17:
            currentProduct = int(y) * int(x[p + 1]) * int(x[p + 2]) * int(x[p + 3])
            if currentProduct > highestProduct:
                print(currentProduct)
                highestProduct = currentProduct
        else:
                break
            p += 1

'generator' object is not subscriptable

Answer 1

Your x value is is a generator object, which is an Iterator: it generates values in order, as they are requested by a for loop or by calling next(x).

You are trying to access it as though it were a list or other Sequence type, which let you access arbitrary elements by index as x[p + 1].

If you want to look up values from your generator's output by index, you may want to convert it to a list:

x = list(x)

This solves your problem, and is suitable in most cases. However, this requires generating and saving all of the values at once, so it can fail if you're dealing with an extremely long or infinite list of values, or the values are extremely large.

If you just needed a single value from the generator, you could instead use itertools.islice(x, p) to discard the first p values, then next(...) to take the one you need. This eliminate the need to hold multiple items in memory or compute values beyond the one you're looking for.

import itertools

result = next(itertools.islice(x, p))