input: Write a function to find the sum of a given list of numbers. The function should return the sum as an integer. If the list is empty, it should return 0.
  
  assert sum_list([1, 2, 3, 4, 5])==15
  assert sum_list([-1, -2, -3, -4, -5])==-15
  assert sum_list([0, 0, 0, 0, 0])==0
  assert sum_list([])==0
output: def sum_list(numbers):
      return sum(numbers) if numbers else 0