用python如何实现学生成绩管理系统？

class Node(object):
 def __init__(self, data, pointer):
 self.data = data
 self.next = pointer


# 创建单链表
class SingleLinkedList(object):
 def __init__(self):
 self.head = Node(None, None)
 self.point = self.head

 def append(self, data):
 # 末尾追加节点
 new_node = Node(data, None)
 self.point.next = new_node
 self.point = new_node

 def insert(self, data, find):
 # 插入数据(前向插入数据)
 if not self.head.next:
  print('链表为空')
  return None
 new_node = Node(data, None)
 self.point = self.head
 while self.point.next.data != find:
  self.point = self.point.next
  if self.point.next is None:
  print('没有找到该元素')
  return None

 new_node.next = self.point.next
 self.point.next = new_node

 def delete(self, find):
 # 删除节点
 # 空链表
 if not self.head.next:
  print('链表为空')
  return None
 self.point = self.head
 while self.point.next.data != find:
  self.point = self.point.next
 pointer = self.point.next
 self.point.next = self.point.next.next
 del pointer

 def insert_after_head(self, data):

 node = Node(data, None)
 # bug 产生没写 if 返回
 if not self.head.next:
  self.head.next = node
  return None
 node.next = self.head.next
 self.head.next = node

 def reverse(self):
 local_list = SingleLinkedList()
 self.point = self.head
 count = 0
 while self.point.next:
  count += 1
  self.point = self.point.next
  data = self.point.data
  local_list.insert_after_head(data)
 return local_list

 def get_size(self):
 count = 0
 self.point = self.head
 while self.point.next:
  self.point = self.point.next
  count += 1
 return count

 def delete_by_tail(self, num):
 size = self.get_size()
 assert (num <= size)
 assert (num > 0)
 pos = size - num
 count = 0
 self.point = self.head
 while count < size:
  count += 1
  self.point = self.point.next
  if count == pos:
  pointer = self.point.next
  self.point.next = self.point.next.next
  del pointer

 # 求中间节点 只允许遍历一次
 def quick_middle(self):
 slow_point = self.head
 fast_point = self.head
 while fast_point.next.next:
  slow_point = slow_point.next
  fast_point = fast_point.next.next
  if not fast_point.next:
  break
 if fast_point.next:
  slow_point = slow_point.next
 return slow_point.data

 def check_circle(self):
 pass

 def sort(self):
 # get_size()改变了 self.point 的指向
 length = self.get_size()
 i, j = 0, 0
 flag = 1
 while i < length:
  self.point = self.head.next
  while j < length - i - 1:
  if self.point.data > self.point.next.data:
   temp = self.point.data
   self.point.data = self.point.next.data
   self.point.next.data = temp
  self.point = self.point.next
  j += 1
  flag = 0
  if flag:
  break
  i += 1
  j = 0

 def print(self):
 # 打印结点
 self.point = self.head
 while self.point.next:
  self.point = self.point.next
  print('{} ->'.format(self.point.data), end=' ')
 print('')


class StudentControlSystem(SingleLinkedList):
 # 打印菜单
 def print_menu(self):
 print('*' * 30)
 print('-' * 13 + '菜单' + '-' * 13)
 print('1.增加学生信息')
 print('2.删除学生信息')
 print('3.修改学生信息')
 print('4.查找学生信息')
 print('5.显示所有信息')
 print('6.排序')
 print('0.退出程序')
 print('*' * 30)

 # 用户输入
 def user_input(self, item):
 try:
  item = int(item)
 except:
  pass
 # 增加信息
 if item == 1:
  self.add_info()
 # 删除信息
 elif item == 2:
  find = input('请输入删除的学号：')
  self.del_info(find=find)
 # 修改信息
 elif item == 3:
  self.modify_info()
 # 查找信息
 elif item == 4:
  self.search_info()
 # 显示信息
 elif item == 5:
  self.display_info()
 # 信息排序
 elif item == 6:
  self.rank_info()
 # 退出程序 保存数据
 elif item == 0:
  with open('database.txt', 'w') as f:
  self.point = self.head
  while self.point.next:
   self.point = self.point.next
   f.writelines('{}\n'.format(self.point.data))
  exit()
 else:
  print('请输入正确的数字')

 # id 保证互异性
 def unique_id(self, std_id):
 self.point = self.head
 while self.point.next:
  self.point = self.point.next
  if self.point.data['id'] == std_id:
  return False
 return True

 # 增加信息
 def add_info(self):
 # id 不能重复
 # 成绩不能超出范围
 name = input('姓名：')
 std_id = input('学生id：')
 while not self.unique_id(std_id=std_id):
  print('id重复')
  std_id = input('学生id：')
 grade = input('学生成绩：')
 if eval(grade) < 0 or eval(grade) > 100:
  print('超出范围')
  grade = input('学生成绩：')
 print(name, std_id, grade)
 print('请确认无误后保存')
 choice = input('y/n')
 items = ['y', 'yes', 'Y', 'Yes']
 if choice in items:
  print(choice)
  data = {'id': std_id, 'name': name, 'grade': grade}
  self.append(data)

 # 删除信息
 def del_info(self, find):
 print('请确认无误后保存')
 choice = input('y/n')
 items = ['y', 'yes', 'Y', 'Yes']
 if choice in items:
  if not self.head.next:
  print('链表为空')
  return None
  self.point = self.head
  while self.point.next.data['id'] != find:
  self.point = self.point.next
  pointer = self.point.next
  self.point.next = self.point.next.next
  del pointer

 # 序列逆序
 def reverse(self):
 local_list = StudentControlSystem()
 self.point = self.head
 count = 0
 while self.point.next:
  count += 1
  self.point = self.point.next
  data = self.point.data
  local_list.insert_after_head(data)
 return local_list

 # 序列排序
 def sort(self, item):
 length = self.get_size()
 i, j = 0, 0
 flag = 1
 while i < length:
  self.point = self.head.next
  while j < length - i - 1:
  if int(self.point.data[item]) > int(self.point.next.data[item]):
   # self.point.data, self.point.next.data =
   # self.point.next.data, self.point.data
   temp = self.point.data
   self.point.data = self.point.next.data
   self.point.next.data = temp
  self.point = self.point.next
  j += 1
  flag = 0
  if flag:
  break
  i += 1
  j = 0

 # 修改信息
 def modify_info(self):
 find = input('输入需要修改的学生的id：')
 if not self.head.next:
  print('链表为空')
  return None
 self.point = self.head
 while str(self.point.next.data['id']) != find:
  self.point = self.point.next
  if self.point.next is None:
  print('没有找到该元素')
  return None
 name = input('姓名：')
 grade = input('学生成绩：')
 self.point.next.data['name'] = name
 self.point.next.data['grade'] = grade

 # 搜索信息
 def search_info(self):
 find = input('输入需要查找的学生的id：')
 if not self.head.next:
  print('链表为空')
  return None
 self.point = self.head
 while str(self.point.next.data['id']) != find:
  self.point = self.point.next
  if self.point.next is None:
  print('没有找到该元素')
  return None
 data = self.point.next.data
 print('ID 姓名 成绩')
 print('{} {} {}'.format(data['id'], data['name'], data['grade']))

 # 信息排序
 def rank_info(self):
 choice = input('1.成绩排序 2.学号排序：')
 order = input('1.升序 2.降序：')
 if choice == '1':
  item = 'grade'
 elif choice == '2':
  item = 'id'
 else:
  return None
 self.sort(item=item)
 if order == '2':
  temp = self.reverse()
  temp.display_info()
  return None
 self.display_info()

 # 显示信息
 def display_info(self):
 self.point = self.head
 print('ID 姓名 成绩')
 while self.point.next:
  self.point = self.point.next
  data = self.point.data
  print('{} {} {}'.format(data['id'], data['name'], data['grade']))
 print('')


def main():
 SCS = StudentControlSystem()
 try:
 with open('database.txt', 'r') as f:
  for data in f.readlines():
  SCS.append(eval(data))
 except:
 with open('database.txt', 'w') as f:
  pass

 while True:
 SCS.print_menu()
 item = input('请输入你的选择：')
 SCS.user_input(item)


if __name__ == "__main__":
 main()