input: Write a function to calculate the average of a list of numbers in Python. If the list is empty, return 0.
  def avg_list(lst):
   if not lst:
    return 0
   sum = 0
   for i in lst:
    sum += i
   avg = sum / len(lst)
   return avg
  
  assert avg_list([1, 2, 3, 4, 5])==3.0
  assert avg_list([0, 0, 0, 0])==0.0
  assert avg_list([10])==10.0
  assert avg_list([])==0
  assert avg_list([-1, -2, -3, -4, -5])==-3.0
output: def avg_list(lst):
   if not lst:
    return 0
   sum = 0
   for i in lst:
    sum += i
   avg = sum / len(lst)
   return avg