input: Write a function to calculate the average of a list of numbers in Python.
  def avg_list(lst):
   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([10,20,30,40]) == 25.0
  assert avg_list([5]) == 5.0
  assert avg_list([]) == 0
  assert avg_list([-1,0,1]) == 0.0
output: def avg_list(lst):
      if not lst:
          return 0
      sum = 0
      count = 0
      for i in lst:
          sum += i
          count += 1
      avg = sum / count
      return avg