input: Write a function to calculate the average of a list of numbers. If the list is empty, return 0.
  def avg_list(lst):
      if not lst:
          return 0
      total = sum(lst)
      return total / len(lst)
      
  assert avg_list([1, 2, 3, 4, 5]) == 3.0
  assert avg_list([10, 20, 30, 40]) == 25.0
  assert avg_list([0, 0, 0, 0]) == 0.0
  assert avg_list([-1, -2, -3, -4, -5]) == -3.0
  assert avg_list([]) == 0
output: def avg_list(lst):
      if not lst:
          return 0
      total = sum(lst)
      return total / len(lst)