input: Write a function to find the sum of a given list of numbers. If the list is empty, return 0.
  assert sum_list([3, 4, 5, 1, 2])==15
  assert sum_list([3, 5, 10, 1, 2])==21
  assert sum_list([4, 3, 1, 2])==10
  assert sum_list([3, 5, 4, 1, 2])==15
  assert sum_list([])==0
output: def sum_list(numbers):
      if not numbers:
          return 0
      return sum(numbers)