input: Write a function to calculate the average of a list of numbers in Python. The function should take a list of numbers as input, sum all the numbers, count the total amount of numbers, and then return the average. 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([-5, -2, 1, 2]) == -1.0
  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