OOP – Private Attributes (underscore convention)

Name:

Date:

Class:

Quick Questions

Shade in the A or B circle for each question.

1. What does a single underscore _ prefix mean?

A Convention: internal use, don't access directly

B The variable is deleted

2. Does Python enforce single-underscore privacy?

A Yes you can't access it

B No it's just a convention

3. What does double underscore __ do?

A Deletes the variable

B Name mangling makes it harder to access

4. Why use getters and setters?

A To control and validate access to attributes

B They're faster

5. def get_balance(self): what is this?

A A getter method that returns the balance

B A constructor

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1obj.__balance		AError: Use snake_case: get_balance
2def getBalance(self):		BError: Double underscore triggers name mangling
3self._balance		COk: Getter method to access private data
4def get_balance(self):		DOutput: 1
510 // 3		EOutput: 3
610 % 3		FValid: Single underscore signals internal use

Definitions

_variable

Fill in the Blanks

Complete each line of code by filling in the missing parts.

class Account: def ________(self, bal): self._balance = bal

class Account: def get_balance(____): return self._balance

class Account: def deposit(self, amount): if amount _ 0: self.________ += amount

class Secret: def ________(self, val): self.__val = val

acc = Account(100) print(acc.___________( ))

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A acc = BankAccount(100)

B acc._balance = -500

C print(acc.get_balance())

Question 2

A class Account:

B def __init__(self, bal):

C self.__balance = bal

E acc = Account(100)

F print(acc.__balance)

Question 3

A class Account:

B def deposit(self, amount):

C self._balance += amount

Question 4

A class Person:

B def __init__(self, age):

C self._age = age

D def set_age(self, age):

E self._age = age

Question 5

A class Account:

B def __init__(self, bal):

C self._balance = bal

D def get_balance():

E return self._balance

Answer Key

OOP – Private Attributes (underscore convention)

Section A: Quick Questions

A — Convention: internal use, don't access directly

B — No it's just a convention

B — Name mangling makes it harder to access

A — To control and validate access to attributes

A — A getter method that returns the balance

Section B: Match the Pairs

obj.__balance → Error: Double underscore triggers name mangling

def getBalance(self): → Error: Use snake_case: get_balance

self._balance → Valid: Single underscore signals internal use

def get_balance(self): → Ok: Getter method to access private data

10 // 3 → Output: 3

10 % 3 → Output: 1

Section C: Definitions

_variable — Convention for internal use - don't access directly from outside the class.~~__variable

Section D: Fill in the Blanks

class Account:
    def __init__(self, bal):
        self._balance = bal

class Account:
    def get_balance(self):
        return self._balance

class Account:
    def deposit(self, amount):
        if amount > 0:
            self._balance += amount

class Secret:
    def __init__(self, val):
        self.__val = val

acc = Account(100)
print(acc.get_balance(  ))

Section E: Spot the Error

B — Directly setting _balance bypasses validation. Use deposit() method.

F — __balance is name-mangled. Access through a getter method.

C — No validation should reject negative deposits

E — Setter has no validation should check age > 0

D — Missing self parameter in get_balance method