input: def largest_number_in_list(numbers: List[int]) -> int:
      """ Find and return the largest number in the given list of integers.
      >>> largest_number_in_list([1000, 506, 299, 620, 35])
      1000
      >>> largest_number_in_list([1, 5, 2, 6, 3])
      6
      """
output:     if not numbers:
          return None
      max_num = numbers[0]
      for num in numbers:
          if num > max_num:
              max_num = num
      return max_num