Python Fastest way to find Indexes of item in list

Question

If one was to attempt to find the indexes of an item in a list you could do it a couple different ways here is what I know to be the fastest

aList = [123, \'         


        

Answer 1

D=dict()
for i, item in enumerate(l):
    if item not in D:
        D[item] = [i]
    else:
        D[item].append(i)

Then simply call D[item] to get the indices that match. You'll give up initial calculation time but gain it during call time.