input: 
  def smallest_number(nums: List[int]) -> int:
      """ Find and return the smallest number in the given list of integers.
      >>> smallest_number([4, 5, 6, 7, 8])
      4
      >>> smallest_number([-10, 0, 3, 20])
      -10
      """
  
output:     if not nums:
          raise ValueError("The list is empty")
      min_num = nums[0]
      for num in nums:
          if num < min_num:
              min_num = num
      return min_num