input: Write a function to suggest an improvement for the provided Python code for finding the sum of elements of a list. The function should return the improved code as a string. If the input list is empty, the function should return a message indicating that the list is empty.
  assert sum_elements([1, 2, 3, 4, 5]) == "return sum(arr) # return sum of elements of arr with one line of code."
  assert sum_elements([]) == "The list is empty."
output: def sum_elements(arr):
      if not arr:
          return "The list is empty."
      return "return sum(arr) # return sum of elements of arr with one line of code."