input: Write a function to determine the total sum of all elements in 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([])==0
  assert calculate_sum_of_list([-1, -2, -3, -4])==-10
  assert calculate_sum_of_list([5, 10, 15, 20])==50
  assert calculate_sum_of_list([100])==100
output: def calculate_sum_of_list(arr):
      total_sum = 0
      for item in arr:
          total_sum += item
      return total_sum