combine_periods.py

import itertools
from typing import Iterable


def apply_period(word: str, positions: Iterable[int]) -> str:
    for index, position in enumerate(positions):
        position += index
        word = word[:position] + "." + word[position:]
    return word


def get_periods(word: str, max_periods: int) -> Iterable[str]:
    all_possible_periods = itertools.chain.from_iterable(
        itertools.combinations(range(1, len(word)), periods)
        for periods in range(1, max_periods + 1)
    )

    return (apply_period(word, periods) for periods in all_possible_periods)


for w in get_periods("helloworld", 3):
    print(w)