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 not lst:
          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
  assert avg_list([10, 15, 20]) == 15.0
  assert avg_list([]) == 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