Not saving data to .db in python?

Question

[MrX]

The question is, when I want to add a new student, the code doesn't save the student's data to a .db file? The .db file was created but empty.. a.save() doesn't work, you have to save with id. Here is the full code:

import shelve
        
        class Student():
            path = 'Students'
            def __init__(self, name, age, mark, level, id=None):
                self.name = name
                self.age = age
                self.mark = mark
                self.level = level
                self.id = id
            
            @property
            def name(self):
                return self.__name
        
            @name.setter
            def name(self, name):
                if isinstance(name,str) and name.isalpha():
                    self.__name = name
                else:
                    self.__name = "Error"
            
            @property
            def age(self):
                return self.__age
            
            @age.setter
            def age(self, age):
                if isinstance(age, int) and age > 0 and age < 120:
                    self.__age = age
                else:
                    self.__age = 0
            
            @property
            def mark(self):
                return self.__mark
            
            @mark.setter
            def mark(self, mark):
                if isinstance(mark, int) and mark > 0 and mark < 10:
                    self.__mark = mark
                else:
                    self.__mark = 0
        
            @property
            def level(self):
                return self.__level
            
            @level.setter
            def level(self, level):
                if isinstance(level, int) and level > 0 and level < 5:
                    self.__level = level
                else:
                    self.__level = 0
            
            def save(self):
                with shelve.open(Student.path) as students:
                    keys = list(students.keys())
                    if len(keys) > 0:
                        id = int(keys[-1]) + 1
                        students[str(id)] = self
                    else:
                        id = 1
                    self.id = str(id)
            
            def update(self):
                with shelve.open(Student.path) as students:
                    students[self.id] = self
        
            def objects():
                objs = []
                with shelve.open(Student.path) as students:
                    for item in students.values():
                        objs.append(item)
                return objs
            
            def get_by_id(id):
                with shelve.open(Student.path) as students:
                   return students[id]
                    
            def __str__(self) -> str:
                return f'{self.id} {self.name} {self.age} {self.mark} {self.level}'
        
        
        def printList():
            for student in Student.objects():
                print(student)
        
        def Filtr():
            print("       Filter      ")
            print("1.Name")
            print("2.Level")
            print("3.Age")
            print("4.Mark")
            n = int(input("Answer: "))
        
            lpeopl = []
            if n > 0 and n <= 4:
                if n == 1:
                    n = input("Enter the first letter of the name you want to find in the list: ")
                    
                    for item in Student.objects():
                        if item.name.startswith(n):
                            lpeopl.append(item)
        
                    if len(lpeopl) != 0:
                        for item in lpeopl:
                            print(item)
        
                elif n == 2:
                    n = input("Enter a level: ")
                    for item in Student.objects():
                        if item.level==n:
                           print(item)
                        
                     
                elif n == 3:
                    n=int(input("Enter an age:"))
                    for item in Student.objects():
                        if item.age==n:
                            print(item)
                
                elif n == 4:
                    n=int(input("Enter a mark:"))
                    for item in Student.objects():
                        if item.mark==n:
                            print(item)
                        
            else:
                print("Select 1 of menu")
        
        def menu():
            print("1. Display a list of students")
            print("2. Add a new student")
            print("3. Filter student")
            javob = int(input("Answer: "))
            if javob == 1:
                printList()
            elif javob == 2:
                ism = input("Name: ")
                age = int(input("Age: "))
                mark = int(input("Mark: "))
                level = int(input("Level: "))
                a = Student(ism, age, mark, level)
                a.save()
                printList()
            elif javob == 3:
                Filtr()
    menu()

Comments

[Сергей Горностаев]

Здесь можно и на русском спрашивать.

[Александр Нестеров]

Сергей Горностаев, судя по профилю - человек из Узбекистана.
Честно говоря, не в курсе как там обстоят с русским, но предположу что английский он знает лучше русского.

[AVKor]

AlexNest, Пусть учит, если не знает. Или идёт туда, где принято спрашивать на английском.

Answer 1

[MrX]

I figured out what's wrong. The error is that I forgot to put update() in the code after a.save()

Answer 2

[Vindicar]

if len(keys) > 0:
    id = int(keys[-1]) + 1
    students[str(id)] = self #you actually save the data here
else:
    id = 1
    # where is the save operation if the db is empty?

You should conditionally determine the id value, then UNconditionally assign it to self.id and save the entire instance to shelve.

Comments

[MrX]

I figured out what's wrong. The error is that I forgot to put update() in the code after a.save()

[Vindicar]

MrX, that does about the same thing, except in a more convoluted way. I'd say save() should be self-reliant, and update() is not even needed, because it does the same thing as save(). So simplify your code by fixing save() and you can drop the update() entirely.