input: Write a function to calculate the sum of a list of numbers. The function should take a single argument, a list of numbers, and return an integer representing the sum of those numbers.
  
  assert sum_list([1, 2, 3]) == 6
  assert sum_list([-1, 0, 1]) == 0
  assert sum_list([10, 20, 30, 40]) == 100
  assert sum_list([]) == 0
  assert sum_list([5]) == 5
output: def sum_list(numbers):
      return sum(numbers)