input: Write a function to improve the provided python code for finding the sum of elements of a list. The original code uses a loop to accumulate the sum. The improved code should use a built-in function to achieve the same result in one line.
  
  ### Input:
  def sum_elements(arr):
      sum_value = 0
      for num in arr:
          sum_value += num
      return sum_value
  
  ### Output:
  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([10, 20, 30]) == 60
  assert sum_elements([]) == 0
  assert sum_elements([-1, -2, -3]) == -6
  assert sum_elements([5]) == 5
output: def sum_elements(arr):
      return sum(arr)