We can put classes in each other. This solution is used for logically grouping related classes, enhancing encapsulation by restricting visibility (as the inner class is only accessible within the outer class), and improving code organization. Inner classes have access to the outer class's objects. The example below perfectly represents all three applications of nested classes.

class BankAccount:
    def __init__(self, balance):
        self.__balance = balance # private attribute

    def getBalance(self):
        return self.__balance

    def updateBalance(self, amount):
        self.__balance += amount

    def start(self, interestRate):
        self.__interest = self.Interest(interestRate, self)

    class Interest: # nested / inner class
        def __init__(self, interestRate, bankacc):
            self.__interestRate = interestRate # private attribute
            bankacc.updateBalance((bankacc.getBalance() * self.__interestRate) / 100)

bankacc = BankAccount(1000)
print(bankacc.getBalance())
bankacc.start(5)
print(bankacc.getBalance())