input: Write a function to calculate the average of a list of numbers in Python. If the input list is empty, the function should 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([10, 20, 30]) == 20.0
  assert avg_list([0, 0, 0]) == 0.0
  assert avg_list([7]) == 7.0
  assert avg_list([]) == 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