Dictionary from a list failed, help needed

[Pedroski55]

I don't know anything about dict.setdefault() or where it might be useful.

You could achieve the same result like this:

mylist = ["a", "b", "c", "a", "c"]
# make a dictionary of empty lists
mydict = {l:[] for l in mylist}
# populate the lists
for v, k in enumerate(mylist):
    mydict[k].append(v)

How to put these 2 steps in a one-liner, I don't know!