input: Write a function to find the sum of elements of a list and return the sum value. Use the built-in `sum` function to simplify the code.
  def sum_elements(arr):
      return sum(arr) # return sum of elements of arr with one line of code.
  assert sum_elements([1, 2, 3, 4, 5])==15
  assert sum_elements([0, 0, 0, 0])==0
  assert sum_elements([-1, 1, -2, 2])==0
  assert sum_elements([])==0
output: def sum_elements(arr):
      return sum(arr)