input: Write a python function to identify the highest positive number in a provided list.
  assert highest_positive([1, 2, 3, 4, -1]) == 4
  assert highest_positive([0, 1, 2, -5, -1, 6]) == 6
  assert highest_positive([0, 0, 1, 0]) == 1
output: def highest_positive(lst):
      return max([num for num in lst if num > 0])