input: 
  def find_smallest_number(nums):
      """ Find the smallest number in a given list.
      >>> find_smallest_number([4, 5, 6, 7, 8])
      4
      """
  
output:     if not nums:
          return None
      smallest = nums[0]
      for num in nums:
          if num < smallest:
              smallest = num
      return smallest