input: Write a function to calculate the average of a list of numbers in Python. If the list is empty, return 0.
  assert avg_list([1, 2, 3, 4, 5])==3.0
  assert avg_list([10, 20, 30, 40, 50])==30.0
  assert avg_list([0, 0, 0, 0])==0.0
  assert avg_list([-1, -2, -3])==-2.0
  assert avg_list([])==0
output: def avg_list(numbers):
      if not numbers:
          return 0
      return sum(numbers) / len(numbers)