Basic usage
Input
c = SecureCounter(3) c.increment() c.value
Output
4
Create a counter starting at 3, increment by 1 (default) and read the value property which returns 4.
Full lesson preview
Protect Internal State with Name Mangling
Learn to keep an object's internal state private using Python's name mangling (double-underscore) and expose a safe public API.
Python practice24 minEncapsulation & Access PatternsAdvancedLast updated April 8, 2026
Problem statement
You will implement a SecureCounter class that keeps its numeric state hidden using Python's name mangling (a double-underscore attribute like __count). The class should provide safe methods to increment, decrement (never allowing the counter to go below zero), read the value via a property, and transfer an amount to another SecureCounter. The goal is to practice encapsulation: the internal state must be stored in a name-mangled attribute and not exposed as a plain public attribute.
Task
Implement a class that uses a name-mangled attribute to store internal state, and provide controlled read/write operations through methods and properties.
Examples
Input format
You will construct and call methods on the SecureCounter class. Examples: SecureCounter(5).increment(), SecureCounter(2).decrement(1), etc.
Output format
Return values from method calls or the value property. The tests compare the string form of the returned value.
Constraints
Do not expose the internal numeric state as a public attribute. Store it using a name-mangled attribute (e.g. self.__count). decrement must clamp at 0 (never negative). Methods should return sensible values: increment/decrement return the new integer value; value is a read-only property; transfer_to modifies both counters.
Samples
Sample 1
Input
SecureCounter(3).increment()
Output
4
Incrementing a counter starting at 3 by the default 1 returns 4.