input: >>> def avg_list(lst):
   sum = 0
   count = 0
   for i in lst:
    sum += i
    count += 1
   avg = sum / count
   return avg
  
  ### Example:
  >>> avg_list([1, 2, 3, 4, 5])
  3.0
  >>> avg_list([10, 20, 30])
  20.0
output:     if count == 0:
          return 0.0