input: Write a function to improve the given Python code for finding the sum of elements of a list using a more efficient method. Implement the function `sum_elements` to return the sum of elements in the list `arr` with a one-liner. Use the `sum()` function to achieve this.
  
  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([5, 10, 15, 20]) == 50
  assert sum_elements([0]) == 0
  assert sum_elements([-1, -2, -3, -4]) == -10
  assert sum_elements([]) == 0
output: def sum_elements(arr):
      return sum(arr)