Properties & Encapsulation

Introduction

Python doesn't enforce private attributes — convention uses _underscore. Use @property for managed access without breaking callers.

Understanding the topic

Core concepts to understand:

• _x — convention for internal.
• __x — name-mangled (rarely used).
• @property turns method into attribute.
• @x.setter for write access.

Syntax reference

Visual flow / code:

class Temperature:
    def __init__(self, celsius: float):
        self._celsius = celsius

    @property
    def celsius(self) -> float:
        return self._celsius

    @celsius.setter
    def celsius(self, value: float):
        if value < -273.15:
            raise ValueError("Below absolute zero")
        self._celsius = value

    @property
    def fahrenheit(self) -> float:
        return self._celsius * 9/5 + 32

t = Temperature(25)
print(t.fahrenheit)  # 77.0

Execution workflow

Real-world use

Properties let you start with simple public attributes, then add validation / computation later without breaking your API. This is huge for library design.

Best practices

• Start with public attrs; add @property only when logic appears.
• Underscore signals internal — don't enforce.

Hands-on exercise

Interview preparation — practice these questions:

• What is @property?
• Public vs private in Python?
• Why no real private?

Summary

In summary: @property = invisible upgrade path. Convention > enforcement.