input: Write a function to calculate the sum of all even numbers in a given list of integers. The function should take a list of integers as input and return the sum of the even numbers. If the list is empty, the function should 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, -4, -6, -8])==-20
output: def sum_even_numbers(lst):
      return sum(num for num in lst if num % 2 == 0)