How to find all the indexes of all the occurrences of a substring in a string

Question

I am wondering if this is even possible without making any import method. But in a given string it is possible to make a list of all the indexes of all the occurrences.

For instance:

s = 'AACATGAACAAG'

for the occurrence AA the output should be:

result = [0, 6, 9]

which are al the positions...