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 and return the average of those numbers. If the list is empty, the function should 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([-1, -2, -3, -4, -5]) == -3.0
  assert avg_list([]) == 0
output: def avg_list(numbers):
      if not numbers:
          return 0
      return sum(numbers) / len(numbers)