input: Write a python function to filter positive numbers from a list.
  assert filter_positive([-1, -2, 5, 0, 6, 8, 4, 9]) == [5, 6, 8, 4, 9]
  assert filter_positive([-10, -20, -30]) == []
  assert filter_positive([0, 1, 2, 3, -1, -2, -3]) == [1, 2, 3]
output: def filter_positive(numbers):
      return [num for num in numbers if num > 0]