input: Write a function to calculate the sum of even numbers in a list.
  assert get_even_sum([1, 2, 3, 4, 5, 6]) == 12
  assert get_even_sum([10, 21, 32, 43, 54]) == 96
  assert get_even_sum([5, 7, 9, 8, 6, 4, 3]) == 18
output: def get_even_sum(lst):
      return sum(x for x in lst if x % 2 == 0)