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