input: Write a function to sum elements of an array using one line of code.
  assert sum_elements([1, 2, 3, 4, 5]) == 15
  assert sum_elements([10, 20, 30, 40]) == 100
  assert sum_elements([-1, -2, -3, -4]) == -10
output: def sum_elements(arr):
      return sum(arr)