itertools.accumulate but trying to replace lambda with str.join

Question

I'm trying not to use lambda here because of it's performance issues in loops, I know there's uses for lambda but I find this one should have a better alternative.

Original code: this works but I don't like that lambda there.

from itertools import accumulate

s = "lorem ipsum dolor"

print(list(accumulate(s.split(), lambda x, y: f'{x} {y}')))
#["lorem", "lorem ipsum", "lorem ipsum dolor"]

I have tried the following:

print(list(accumulate(s.split(), ' '.join)))

I must be missing something small here that will make me feel like an idiot. It has to be just a simple matter of packing the tuple I assume.

Answer 1

The str.join method expects an iterable as an argument, and yet accumulate passes to it two arguments for each iteration, hence the error. You can use the str.format method instead:

print(list(accumulate(s.split(), '{} {}'.format)))