cut_substr_naive.py

haystack = [1, 2, 3, 2, 1, 2, 3, 4, 5, 4, 3, 2, 1, 2, 3, 4, 5, 6]
needle = [2, 1, 2]


def cut_substr_once(substr, string):
  substr_size = len(substr)
  for ind, _ in enumerate(string):
    if substr == string[ind: ind + substr_size]:
      return string[:ind], string[ind + substr_size:]

  return string, None


def cut_substr(substr, string):
  tail, result = string, []
  while tail:
    head, tail = cut_substr_once(substr, tail)
    result.extend(head)

  return result


print(cut_substr(needle, haystack))