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 len(lst) == 0:
    return 0
   sum = 0
   count = 0
   for i in lst:
    sum += i
    count += 1
   avg = sum / count
   return avg
  
  assert avg_list([1, 2, 3, 4, 5])==3.0
  assert avg_list([0, 0, 0, 0])==0.0
  assert avg_list([5, 10, 15, 20])==12.5
  assert avg_list([])==0.0
  assert avg_list([-1, -2, -3, -4, -5])==-3.0
output: def avg_list(lst):
   if len(lst) == 0:
    return 0
   sum = 0
   count = 0
   for i in lst:
    sum += i
    count += 1
   avg = sum / count
   return avg