missing 2 required positional arguments

Question

My code wont work and it keeps repeating these error. "TypeError: years_of_employment() missing 2 required positional arguments: 'self' and 'current_year.
What I tried to do was create a class that inherited from superclass and try information hiding. Here's the code.

class Person:
    def __init__(self, first_name, last_name, birth_year, salary, employed_year):
        self.__first_name = first_name
        self.__last_name = last_name
        self.__birth_year = birth_year
        self.__salary = salary
        self.__employed_year = employed_year
    
    @property
    def first_name(self):
        return self.__first_name
    @property
    def last_name(self):
        return self.__last_name
    @property
    def birth_year(self):
        return self.__birth_year
    @property
    def salary(self):
        return self.__salary
    @property
    def employed_year(self):
        return self.__employed_year
    
    def age(self, current_year):
        return f'{current_year - self.birth_year}'        

class Teacher(Person):
    def __init__(self, first_name, last_name, birth_year, salary, employed_year):
        super().__init__(first_name, last_name, birth_year)
        self.salary = salary
        self.employed_year = employed_year

    def __str__(self):
        return f'{self.first_name} {self.last_name} är född {self.birth_year} och tjäner {self.salary} kr/månad'
        
    def years_of_employment(self, current_year):
        return (current_year - self.employed_year) * '*'

person = Person("Jan", "Gran", 1986, 28000 , 2015)
Teacher.years_of_employment()

print(f'{person.first_name} is born {person.birth_year} and earn {person.salary} SEK/month')
print(f'Teacher {person.first_name} is {person.age(2022)} old')
print(f'Number of years of employment: {Teacher.years_of_employment(2022)}')

The answer should be this:
Jan Gran was born in 1986 and earns SEK 28,000 / month The teacher
Jan is 36 years old Number of years of employment:

Answer 1

Like the error says, you haven't provided a Teacher (self) or the current_year.

Create a Teacher, not a Person:

person = Teacher("Jan", "Gran", 1986, 28000 , 2015)

and then you can call its years_of_employment method, passing the current year as the argument:

print(person.years_of_employment(2022))

Note that you have a bug in Teacher.__init__ that will raise another exception when you try to create a Teacher, which is that you don't pass all the necessary parameters to Person.__init__. But since your Teacher doesn't init anything that Person doesn't, you don't need to define a Teacher.__init__ at all -- and all the stuff in Person.__init__ plus all its properties can be implemented automatically by decorating it as a dataclass and just listing all the properties:

from dataclasses import dataclass

@dataclass(frozen=True)
class Person:
    first_name: str
    last_name: str
    birth_year: int
    salary: int
    employed_year: int
    
    def age(self, current_year: int) -> str:
        return f'{current_year - self.birth_year}'        


class Teacher(Person):
    def __str__(self) -> str:
        return f'{self.first_name} {self.last_name} är född {self.birth_year} och tjäner {self.salary} kr/månad'
        
    def years_of_employment(self, current_year: int) -> str:
        return (current_year - self.employed_year) * '*'


person = Teacher("Jan", "Gran", 1986, 28000 , 2015)
print(f'{person.first_name} is born {person.birth_year} and earn {person.salary} SEK/month')
print(f'Teacher {person.first_name} is {person.age(2022)} old')
print(f'Number of years of employment: {person.years_of_employment(2022)}')