input: Write a function to improve the following Python code for finding the sum of elements of a list.
  
  def sum_elements(arr):
      sum_value = 0
      for num in arr:
          sum_value += num
      return sum_value
  
  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([-1, -2, -3, -4, -5])==-15
  assert sum_elements([])==0
output: def sum_elements(arr):
      return sum(arr)