grouping/chunking elements with last_index.

handle_last_index.py

def handle_last_index(elements, last_index):
    grouped = []
    for i, _ in enumerate(last_index):
        if i == 0:
            grouped.append(' '.join(elements[:last_index[i] + 1]))
        elif i == len(last_index) - 1:
            grouped.append(' '.join(elements[last_index[i - 1] + 1:]))
        else:
            grouped.append(' '.join(elements[last_index[i - 1] + 1:last_index[i] + 1]))

    return grouped


print(handle_last_index(['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h'], [2, 5, 7]))
# ['a b c', 'd e f', 'g h']

print(handle_last_index(['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h'], [0, 3, 8]))
# ['a', 'b c d', 'e f g h']