4.3 Methods and Encapsulation | Code Scholars Tutoring

How it works

Python marks intended privacy by naming convention rather than enforcement, so encapsulation is a contract between programmers.

Expose behavior through methods and treat underscore-prefixed names as internal.

Common error

Assuming a leading underscore prevents access. It signals intent only.

Worked example

Python

class Wallet:
    def __init__(self):
        self._balance = 0
    def deposit(self, amount):
        if amount > 0:
            self._balance += amount
    def balance(self):
        return self._balance

w = Wallet()
w.deposit(8)
w.deposit(-2)
print(w.balance())

Output

Methods enforce the intended update rule. A leading underscore communicates non-public implementation by convention; it does not create an impenetrable access boundary.

Exercises

4.3.1 · Explain

Why is directly changing _balance weaker than using deposit for normal client code?

Show solution

It bypasses the method validation and couples the caller to internal representation. Respect the public interface even when the language permits direct access.

4.3.2 · Write code

Write a Celsius class with a method returning Fahrenheit, and show the result for 0 degrees Celsius.

Show solution

Use the conversion inside an instance method.

One valid solution

class Celsius:
    def __init__(self, value):
        self.value = value
    def fahrenheit(self):
        return self.value * 9 / 5 + 32

print(Celsius(0).fahrenheit())

Expected output

32.0

Open Python compiler