1.  

@staticmethod
    def hcf(x,y):
        x=abs(x)
        y=abs(y)
        smaller = y if x>y else x
        s = smaller
        while s>0:
            if x%s==0 and y%s==0:
                break
            s-=1
        return s

2.

class Fraction:
    def __init__(self,nr,dr=1):
        self.nr = nr
        self.dr = dr
        if self.dr < 0:  
            self.nr *= -1
            self.dr *= -1
        self._reduce()

    def show(self):
        print(f'{self.nr}/{self.dr}')

    def multiply(self,other):
        if isinstance(other,int):
            other = Fraction(other)
        f = Fraction(self.nr * other.nr , self.dr * other.dr)
        f._reduce()
        return f
        
    def add(self,other):
        if isinstance(other,int):
            other = Fraction(other)
        f = Fraction(self.nr * other.dr + other.nr * self.dr, self.dr * other.dr)
        f._reduce()
        return f

    def _reduce(self):
        h = Fraction.hcf(self.nr, self.dr)
        if h == 0:
            return
        
        self.nr //= h
        self.dr //= h
        
    @staticmethod
    def hcf(x,y):
        x=abs(x)
        y=abs(y)
        smaller = y if x>y else x
        s = smaller
        while s>0:
            if x%s==0 and y%s==0:
                break
            s-=1
        return s

       
f1 = Fraction(6,36)
f1.show()
f2 = Fraction(2,-12)
f2.show()
f3 = f1.multiply(f2)
f3.show()
f3 = f1.add(f2)
f3.show()
f3 = f1.add(5) 
f3.show()
f3 = f1.multiply(5) 
f3.show()

3.

class SalesPerson:    
    total_revenue = 0
    names = []
    
    def __init__(self,name,age):
        self.name = name
        self.age = age
        self.sales_amount = 0
        SalesPerson.names.append(name)

    def make_sale(self,money):
        self.sales_amount += money
        SalesPerson.total_revenue += money

    def show(self):
        print(self.name, self.age, self.sales_amount)

s1 = SalesPerson('Bob', 25)
s2 = SalesPerson('Ted', 22)
s3 = SalesPerson('Jack', 27)
            
s1.make_sale(1000)
s1.make_sale(1200)
s2.make_sale(5000)
s3.make_sale(3000)
s3.make_sale(8000)

s1.show()
s2.show()
s3.show()

print(SalesPerson.total_revenue)
print(SalesPerson.names)

4.

class Employee:
    domains = set()
    
    def __init__(self,name,email):
        self.name = name
        self.email = email
        domain = email[email.index('@')+1 : ]
        Employee.domains.add(domain)
   
    def display(self):
        print(self.name, self.email)
             
e1 = Employee('John','[email protected]')
e2 = Employee('Jack','[email protected]')
e3 = Employee('Jill','[email protected]')
e4 = Employee('Ted','[email protected]')
e5 = Employee('Tim','[email protected]')
e6 = Employee('Mike','[email protected]')

print(Employee.domains)

5.

class Employee:
    allowed_domains = {'yahoo.com', 'gmail.com', 'outlook.com'}
    
    def __init__(self,name,email):
        self.name = name
        self.email = email
   
    def display(self):
        print(self.name, self.email)

    @property
    def email(self):
        return self._email

    @email.setter
    def email(self, new_email):
        domain = new_email[new_email.index('@')+1 : ]
        if domain in Employee.allowed_domains:
            self._email = new_email
        else:
            raise RuntimeError(f'Domain {domain} is not allowed')
            
e1 = Employee('John','[email protected]')
e2 = Employee('Jack','[email protected]')
e3 = Employee('Jill','[email protected]')
e4 = Employee('Ted','[email protected]')
e5 = Employee('Tim','[email protected]')
e5.display()

e4.email = '[email protected]'
e4.display()

e3.email = '[email protected]'
e3.display()

6.

class Stack:

    MAX_SIZE = 5
        
    def __init__(self):
        self.items = []

    def is_empty(self):
        return self.items == []

    def size(self):
        return len(self.items)

    def push(self, item):
        if self.size() == Stack.MAX_SIZE:
            raise RuntimeError('Stack is full')
        self.items.append(item)

    def pop(self):
        if self.is_empty():
            raise RuntimeError("Stack is empty")
        return self.items.pop()
    
    def display(self):
        print(self.items)


if __name__ == "__main__":
    st = Stack()

    while True:
        print("1.Push") 
        print("2.Pop") 
        print("3.Peek") 
        print("4.Size")
        print("5.Display") 
        print("6.Quit")
         
        choice = int(input("Enter your choice : "))

        if choice == 1:
            x=int(input("Enter the element to be pushed : "))
            st.push(x) 
        elif choice == 2:
            x=st.pop() 
            print("Popped element is : " , x) 
        elif choice == 3:
            print("Element at the top is : " , st.peek()) 
        elif choice == 4:
            print("Size of stack " , st.size()) 
        elif choice == 5:
            st.display()         
        elif choice == 6:
          break;
        else:
          print("Wrong choice") 
        print() 

7.

class BankAccount:

    bank_name = 'ABC bank, XYZ Street, New Delhi'

    def __init__(self, name, balance=0, bank=bank_name):
        self.name = name
        self.balance = balance
        self.bank = bank

    def display(self):
         print(self.name, self.balance, self.bank)

    def withdraw(self, amount):
        self.balance -= amount

    def deposit(self, amount):
        self.balance += amount
    
a1 = BankAccount('Mike', 200, 'PQR Bank Delhi')
a2 = BankAccount('Tom')

a1.display()
a2.display()

Note that here we could use the class variable bank_name without preceding it with the class name.

Any statements that are written inside the class methods, have to use the fully qualified class variable name, for example MyCLass.x.

Any statement that is at the class level, i.e. outside the class methods should use simply the variable name, not the fully qualified name.

For example -

class MyClass():
      x = 6
      y = x + 10       

 So here you need to use it as x, not as MyClass.x