input: Write a function to suggest an improvement for the following Python code that calculates the sum of elements in a list. The original function should be replaced with a more concise and efficient implementation.
  
  ### Original Code:
  def sum_elements(arr):
      sum_value = 0
      for num in arr:
          sum_value += num
      return sum_value
  
  ### Improved 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]) == 10
  assert sum_elements([]) == 0
  assert sum_elements([-1, -2, -3, -4]) == -10
  assert sum_elements([5]) == 5
  assert sum_elements([10, -5, 15, -10]) == 10
output: def sum_elements(arr):
      return sum(arr)