Chunked Iterator: Python Riddle

I really like this python riddle. And it is (almost) a practical problem.

Say you have an iterator (stream of objects of unknown length). And you want to separate it to equal size chunks. An example: splitting a file to multiple smaller sized files.

Doing the same with lists is much easier because the length of the list is known:

from typing import List, TypeVar T = TypeVar('T') def chunks(l: List[T], n: int) -> List[List[T]]: return [l[i:i + n] for i in range(0, len(l), n)] items = list(range(10)) print(chunks(items, 3)) # [[0, 1, 2], [3, 4, 5], [6, 7, 8], [9]] print(chunks(items, 4)) # [[0, 1, 2, 3], [4, 5, 6, 7], [8, 9]]  

The riddle is: write chunks where the input is an iterator. And the output is an iterator of iterators

 def chunks(l: Iterator[T], n: int) -> Iterator[Iterator[T]]: ???? 

I will add the solution later today or tomorrow.

Extra points for run-time performance

Followup question: What problem can you spot in the solution to this problem?

Enjoy

Edit: Solution is here