name 'fullname' is not defined

[witch]

class Person:

    def __init__(self, first, last, fathers_name, age):
        self.first = first
        self.last = last
        self.fathers_name = fathers_name
        self.age = age

    def fullname(self):
        return '{} {} {}'.format(self.first, self.last, self.fathers_name)

class Student(Person):
    def __init__(self, first, last, fathers_name, age, grade, avg_mark):
        super().__init__(first, last, fathers_name, age)
        self.grade = grade
        self.avg_mark = avg_mark

class Workers(Person):
    def __init__(self, fisrt, last, fathers_name, age, positon, pay, wrk_exp):
        super().__init__(first, last, fathers_name, age)
        self.position = position
        self.pay = pay
        self.wrk_exp = wrk_exp

person_1 = Person('Микола', 'Кучварський', 'Миколайович', 56)
fullname(person_1)

Error:
Traceback (most recent call last):
  File "C:/Users/user/AppData/Local/Programs/Python/Python37-32/School 1.py", line 26, in <module>
    fullname(person_1)
NameError: name 'fullname' is not defined

so I`m learning Python OOP and currently Im on classes, now I have this problem, any idea why it does it ?