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()