input: Write a function to filter a list of integers and return only even numbers. If the list contains no even numbers, return an empty list.
  assert filter_even_numbers([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]) == [2, 4, 6, 8, 10]
  assert filter_even_numbers([1, 3, 5, 7, 9]) == []
  assert filter_even_numbers([]) == []
  assert filter_even_numbers([2, 4, 6, 8, 10]) == [2, 4, 6, 8, 10]
  assert filter_even_numbers([3, 4, 5, 7]) == [4]
output: def filter_even_numbers(lst):
      return [num for num in lst if num % 2 == 0]