input: Write a python function to find the largest number in a list.
  assert get_largest([1, 3, 4, 5, 19, 13, 7]) == 19
  assert get_largest([10, 20, 30, 5, 50, 40]) == 50
  assert get_largest([-10, -20, -30, -5, -50, -40]) == -5
output: def get_largest(numbers):
      if not numbers:
          return None
      largest = numbers[0]
      for number in numbers[1:]:
          if number > largest:
              largest = number
      return largest