Add Getter and Setter Methods for an Attribute

Summary

Implement getter and setter methods with simple validation for a private attribute.

Problem statement

Implement a BankAccount class that stores the balance in a private attribute (name-mangled). Provide a get_balance() method that returns the current balance and a set_balance(amount) method that updates the balance only if amount is an integer >= 0. If the update is valid, set_balance should update the private attribute and return self so calls can be chained; if invalid, it should not change the balance and should return None. This exercise teaches controlled access and validation through explicit getter and setter methods.

Task

Create getter and setter methods for a private attribute. The setter should validate input and only update when valid, returning the instance on success and None on failure.

Examples

Input format

A single expression that creates a BankAccount and calls get_balance()/set_balance() (evaluated by the test runner).

Output format

Return numeric balance from get_balance(); set_balance returns the instance on success (so chaining returns a balance) or None on failure (represented as an empty string by the test harness).

Constraints

Balance must be an integer >= 0. Use a private (double-underscore) attribute to store the balance. set_balance should return self on success and None on invalid input.

Samples