input: Write a function to calculate the sum of numbers in a list.
  assert sum_nums([1, 2, 3, 4, 5]) == 15
  assert sum_nums([10, 20, 30, 40, 50]) == 150
  assert sum_nums([0, -1, -2, -3, -4]) == -10
output: def sum_nums(numbers):
      return sum(numbers)