Example of a use case for inheritance

acct.py

class Bank:
    def __init__(self, balance):
        assert balance > 0
        self.balance = balance
    
    def deposit(self, val):
        self.balance += val
    
    def withdraw(self, val):
        if val <= self.balance:
            self.balance -= val

# LoggedBank has identical behavior to Bank,
# Except it ALSO tracks past values to help with testing.
# Testing and 'production' are different contexts.
class LoggedBank(Bank):
    def __init__(self, balance):
        assert balance > 0
        self._balance = balance
        self._history = [balance]

    @property
    def balance(self):
        return self._balance

    @balance.setter
    def balance(self, new_balance):
        self._history.append(new_balance)
        self._balance = new_balance

def run(b: Bank):
    b.deposit(4)
    b.withdraw(3)

if __name__ == "__main__":
    b = Bank(2)
    run(b)
    print(b.balance)

    b = LoggedBank(2)

    # This still typechecks, because we're using a subtype
    run(b)
    print(b.balance)
    print(b._history)

A quick demo of when inheritance can be the right choice. The child class has identical logical behavior to the base class, but has an additional "motive": it can also surface a change history for testing. Since the main code environment doesn't cover the testing context, LoggedBank and Bank have identical behavior throughout the entire codebase, meaning we can freely use LoggedBank in our tests.