class Student:
 def __init__(self,sno,name,english,math):
  self.sno=sno
  self.name=name
  self.__english=english
  self.__math=math
  
 @property
 def english(self):
  return self.__english
  
 @english.setter
 def english(self,english):
  self.__english=english if 0<=english<=100 else 0
  
 @property
 def math(self):
  return self.__math
    
 @math.setter
 def math(self,math):
  self.__math=math if 0<=math<=100 else 0
  
 def get_average(self):
  return (self.english+self.math)/2


 def __str__(self):
  s=str.format('{0:>4d}{1:　>4s}{2:>8d}{3:>8d}',self.sno,self.name,self.english,self.math)
  return s
  
  
 @staticmethod
 def get_header():
  return '{0:>2s}{1:　>4s}{2:\u3000>4s}{3:　>4s}'.format('学号','姓名','英语','数学')
  
 def __eq__(self,other):
  return self.sno==other.sno
  
 def __gt__(self,other):
  return self.sno>other.sno

#测试
if __name__=='__main__':
 s1=Student(1,'王大海',100, 65)
 s2=Student(2,'李三',38,45)
 s3=Student(3,'李四',88,45)
 print(s1>s2)
 students=[s2,s1,s3]
 students.sort()
 print(students)
 print(Student.get_header())
 for s in students:
  print(s) 

from student import Student

class BanJi:
 def __init__(self,name):
  self.name=name
  self.students=[]
  self.load_data()
  
 def load_data(self):
  with open('data.txt','r')as f:
   for line in f:
    d=line.split()
    self.students.append(Student(int(d[0]),d[1],int(d[2]),int(d[3])))
    
 def show_student(self):
  print(Student.get_header())
  for s in self.students:
   print(s)
   
 def add_student(self,student):
  if student in self.students:
   return '此学生已存在'
  else:
   self.students.append(student)
   return'添加成功'
   
 def __index_student(self,sno):
  s=Student(sno,'',0,0)
  if s not in self.students:
   return None
  else:
   return self.students.index(s)
   
 def find_student(self,sno):
  i = self.__index_student(sno)
  if i is None:
   return None
  else:
   return self.students[i]


 def delete_student(self,sno):
  i = self.__index_student(sno)
  if i is None:
   r = '没有学号为{0: d}'.format(sno)
  else:
   del self.students[i]
   r = '删除成功！'
  return r
  
 def update_student(self,sno):
  s = self.find_student(sno)
  if s is None:
   return '没有学号为{0：d}的学生！'.format(sno)
  else:
   print(s)
   print('请输入新的值，直接回车不修改！')
   name_str = input('姓名：')
   english_str = input('英语：')
   math_str = input('数学：')
   s.name = name_str if len(name_str)>0 else s.name
   s.name = int(english_str) if len(english_str)>0 else s.english
   s.name = int(math_str) if len(math_str)>0 else s.math
   return '修改成功！'
   
 def save_data(self):
  with open('data.txt','w',encoding = 'GBK') as f:
   for s in self.students:
    r = str.format('{0:d} {1:s} {2:d} {3:d}\n',s.sno,s.name,s.english,s.math)
    f.write(r)
   
    
 def sort_by_english(self,reverse = False):
  self.students.sort(key=lambda x: x.english,reverse = reverse)

import os
from student import Student
from banji import BanJi

menu = """

*********************

 学生成绩管理系统
 1.浏览学生成绩
 2.按学号查找学生
 3.按英语成绩排序
 4.添加学生
 5.删除学生
 6.修改学生信息
 9.保存
 0.退出
 
*********************

"""
tip = '输入（0-9）选择操作：'

choice = ''

b = BanJi('1802')

os.system('cls')
print(menu)

while True:
 choice = input(tip)
 os.system('cls')
 print(menu)
 if choice == '0':
  print('数据以保存！')
  break
 elif choice == '1':
  b.show_student()
 elif choice == '2':
  sno = int(input('请输入您需要查询的学生的学号：'))
  s = b.find_student(sno)
  if s is None:
   print('无此学号的学生！')
  else:
   print(s)
 elif choice == '3':
  b.sort_by_english()
  b.show_student()
 elif choice == '4':
  print('请输入学生信息：')
  sno = int(input('学号：'))
  name = input('姓名：')
  english = int(input('英语：'))
  math = int(input('数学：'))
  student = Student(sno,name,english,math)
  r = b.add_student(student)
  print(r)
 elif choice == '5':
  sno = int(input('请输入要删除的学生的学号：'))
  r = b.delete_student(sno)
  print(r)
  
 elif choice == '6':
  sno = int(input('请输入要修改的学生的学号：'))
  r = b.update_student(sno)
  print(r)
  
 elif choice == '9':
  b.save_data()
  print('保存成功！')
 else:
  print('输入错误！')