input: Write a function to identify the largest number in a given list.
  
  def find_largest_number(lst):
      if not lst:
          return None
      max_num = lst[0]
      for num in lst:
          if num > max_num:
              max_num = num
      return max_num
  
  assert find_largest_number([1000, 506, 299, 620, 35]) == 1000
  assert find_largest_number([5, 3, 8, 4, 9]) == 9
  assert find_largest_number([7]) == 7
  assert find_largest_number([]) == None
output: def find_largest_number(lst):
      if not lst:
          return None
      max_num = lst[0]
      for num in lst:
          if num > max_num:
              max_num = num
      return max_num