Python | Late to #CLASSES (geddit lel)

Finally, I have gotten the balls to start learning classes, haven't quite got the hang of them, but they are pretty interesting, so, look forward to great things, btw, I still have not given up my goal of creating a snake game before 2013 comes to it's end, I will, trust me, i will.

import math as _math

class Math():
   def __init__(self, x, y):
      self.x = x
      self.y = y
      self.result = 0

   def __str__(self):
       return str(self.result)

class Pythagorus(Math):
    def calculate(self):
        self.result = _math.sqrt(self.x ** 2 + self.y ** 2)

obj = Pythagorus(8,5)
obj.calculate()
print(obj)




class Person():
    def __init__(self, name, age):
        self.name = name
        self.age = age
    def __str__(self):
        return 'Hi! My name is {} and I am {} years old!'.format(self.name,self.age)

class Student(Person):
    def __init__(self, name, age, loans):
        Person.__init__(self, name, age)
        self.loans = loans
    def __str__(self):
        return 'Hi! My name is {} and I am {} years old! But I owe ${} :/'.format(self.name, self.age, self.loans)
person = Student('Samir',16,1002)
print(person)




class Person():
    def __init__(self, name, age):
        self.name = name
        self.age = age
    def __str__(self):
        print('Person - ')
        return "My name is {}. I am {} years old. ".format(self.name, self.age)

class Military(Person):
    def __init__(self, name, age, rank):
        Person.__init__(self, name, age)
        self.rank = rank
    def __str__(self):
        print('Military - ')
        return Person.__str__(self) + "I am a {}".format(self.rank)

class Teacher(Person):
    def __init__(self, name, age, sub):
        print('Teacher - ')
        Person.__init__(self, name, age)
        self.sub = sub
    def __str__(self):
        return Person.__str__(self) + "I teach {}".format(self.sub)

class Student(Person):
    def __init__(self, name, age, loans):
        Person.__init__(self, name, age)
        self.loans = loans



class Animal:
    def __init__(self, name, bark):
        self.name = name
        self.bark = bark
    def Dog(self):
        print('{} is a dog, and dogs go {}!'.format(self.name, self.bark))

    
d1 = Animal('Rufus', 'Woof!')
d1.Dog()




class Person:
    population = 0
    def __init__(self, name, age):
        self.name = name
        self.age = age
        print('{} has been born!'.format(self.name))
        Person.population += 1
    def __str__(self):
        return '{} is {} years old'.format(self.name, self.age)
    def __del__(self):
        print('{} is dying! :('.format(self.name))
        Person.population -= 1
    def totalPop():
        print('There are {} people in the world.'.format(Person.population))

        
p1 = Person('Johnny', 20)
print(Person.population)
p2 = Person('Mary', 27)
print(Person.population)
print(p1)
print(p2)

        


class Student:
    def __init__(self, name):
        self.name = name
        self.attend = 0
        self.grades = []
    def addGrades(self, grade):
        self.grades.append(grade)
    def attendDay(self):
        self.attend += 1
    def getAverage():
        return sum(self.grades) / len(self.grades)