input: Write a function to calculate the average of a list of numbers. If the given list is empty then return 0.
  def avg_list(lst):
   sum = 0
   count = 0
   for i in lst:
    sum += i
    count += 1
   if count == 0:
    return 0
   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([])==0.0
  assert avg_list([10, 20, 30, 40, 50])==30.0
  assert avg_list([1])==1.0 
  assert avg_list([-1, -2, -3, -4, -5])==-3.0
output: def avg_list(lst):
   sum = 0
   count = 0
   for i in lst:
    sum += i
    count += 1
   if count == 0:
    return 0
   avg = sum / count
   return avg