input: Write a function to take a list of integers and return the sum of the even numbers in the list.
  
  assert sum_even_numbers([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]) == 30
  assert sum_even_numbers([-2, 0, 2, 4]) == 4
  assert sum_even_numbers([1, 3, 5, 7]) == 0
  assert sum_even_numbers([]) == 0
output: def sum_even_numbers(numbers):
      return sum(num for num in numbers if num % 2 == 0)