input: Write a function that extracts only the integer elements from a provided list.
  assert extract_integers([]) == []
  assert extract_integers([4, {}, [], 23.2, 9, 'adasd']) == [4, 9]
  assert extract_integers([3, 'c', 3, 3, 'a', 'b']) == [3, 3, 3]
output: def extract_integers(lst):
      return [i for i in lst if isinstance(i, int)]