input: Write a function to calculate the total sum of all elements of a list. If the list is empty, return 0.
  def calculate_sum_of_list(arr):
      total_sum = 0
      for item in arr:
          total_sum += item
      return total_sum
  assert calculate_sum_of_list([1, 2, 3, 4])==10
  assert calculate_sum_of_list([5, 10, 15])==30
  assert calculate_sum_of_list([0, 0, 0])==0
  assert calculate_sum_of_list([])==0
output: def calculate_sum_of_list(arr):
      total_sum = 0
      for item in arr:
          total_sum += item
      return total_sum