input: Write a function that takes a list of numbers as input and prints the result of finding the sum of the list. If the list is empty, the function should print 0. The function should have the header `def sum_list(arr):` and should return the sum of the elements in the list.
  
  assert sum_list([1, 2, 3, 4, 5]) == 15
  assert sum_list([-1, -2, -3, -4, -5]) == -15
  assert sum_list([]) == 0
  assert sum_list([10, 20, 30]) == 60
output: def sum_list(arr):
      return sum(arr)