input: Write a function to compute the sum of a list of numbers. The function should return the sum as an integer.
  assert sum_list([1, 2, 3, 4])==10
  assert sum_list([0, 0, 0])==0
  assert sum_list([-1, 1, -1, 1])==0
  assert sum_list([10, 20, 30])==60
  assert sum_list([])==0
output: def sum_list(numbers):
      return sum(numbers)