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. The function should be named `sum_even_numbers` and take one parameter, `numbers`, which is a list of integers.
  
  assert sum_even_numbers([1, 2, 3, 4, 5, 6, 7, 8, 9, 10])==30
  assert sum_even_numbers([0, 2, 4, 6, 8, 10])==30
  assert sum_even_numbers([1, 3, 5, 7, 9])==0
  assert sum_even_numbers([])==0
output: def sum_even_numbers(numbers):
      return sum(num for num in numbers if num % 2 == 0)