I have created two classes: Person and Student in different modules. Here is my class Person:

import datetime


class Person:

    def __init__(self, name, surname, patronymic, birthdate):
        self.name = name
        self.surname = surname
        self.patronymic = patronymic
        self.birthdate = birthdate

    def age(self):#this function calculates age of person
        today = datetime.date.today()
        age = today.year - self.birthdate.year

        if today < datetime.date(today.year, self.birthdate.month, self.birthdate.day):
            age -= 1

        return age

Here is my class Student:

from ClassPerson import Person


class Student(Person):
    number_of_group = eval(input("\nInput number of group: "))
    summa = 0
    amount_of_students = 0
    overall_age = 0

    def __init__(self, name, surname, patronymic, birthdate, faculty, group, scholarship):
        Person.__init__(self, name, surname, patronymic, birthdate)
        self.faculty = faculty
        self.group = group
        self.scholarship = scholarship
        if Student.number_of_group == self.group:
            Student.summa  = self.scholarship
            Student.overall_age  = Student.age(self)
            Student.amount_of_students  = 1

    @property
        def scholarship(self):
            return self.__scholarship

    @scholarship.setter
    def scholarship(self, new_s):
        if new_s < 1300:
            self.__scholarship = 1300
        elif new_s > 4000:
            self.__scholarship = 4000
        else:
            self.__scholarship = new_s

I have one simple problem: I need to calculate for specific group overall sum of scholarships and middle age of students of this group. I do calculations in def __init__. But i also had property and setter to change the amount of scholarship due to conditions. So for example we have 3 students:

student1 = Student(
    "Joe",
    "Hapfy",
    "Canes",
    datetime.date(1992, 3, 12),
    "Philosophy faculty",
    441,
    4300
)

student2 = Student(
    "Jane",
    "Mers",
    "Rodrigo",
    datetime.date(1998, 4, 29),
    "Historical faculty",
    441,
    2700
)

student3 = Student(
    "Pavlo",
    "Hornov",
    "Andriyovich",
    datetime.date(1997, 7, 22),
    "Mathematics faculty",
    171,
    1300
)

I want to change student1 scholarship. For example:

student1.scholarship = 1500
print(student1.scholarship)

But the changes are not saved, cause i do calculations in dev __init__. For example, I input number of group as 441.

result = Student.overall_age/Student.amount_of_students
print("Total sum of scholarships: %d" % Student.summa)

The sum of scholarships will be 4300 2700, but due to setter 4300 will be changed to 4000 and sum will be 6700. But now my student1 scholarship is 1500 and i want to receive result 1500 2700=4200. How can i do such calculations after changes of scholarship? Should I use method or something like that instead of calculations in dev __init__?

CodePudding user response：

The property setter needs to update Student.summa when necessary.

Since the setter needs to read the old value, we can't use it before we initialize the internal __scholarship attribute. So the __init__() method needs to assign directly to the internal attribute, rather than using the setter with self.scholarship.

from ClassPerson import Person


class Student(Person):
    number_of_group = eval(input("\nInput number of group: "))
    summa = 0
    amount_of_students = 0
    overall_age = 0

    def __init__(self, name, surname, patronymic, birthdate, faculty, group, scholarship):
        Person.__init__(self, name, surname, patronymic, birthdate)
        self.faculty = faculty
        self.group = group
        self.__scholarship = scholarship
        if Student.number_of_group == self.group:
            Student.summa  = self.scholarship
            Student.overall_age  = Student.age(self)
            Student.amount_of_students  = 1

    @property
    def scholarship(self):
        return self.__scholarship

    @scholarship.setter
    def scholarship(self, new_s):
        old_s = self.__scholarship
        if new_s < 1300:
            self.__scholarship = 1300
        elif new_s > 4000:
            self.__scholarship = 4000
        else:
            self.__scholarship = new_s

        # Adjust Student.summa by the change in scholarship
        if self.group == Student.number_of_group:
            Student.summa  = self.__scholarship - old_s