Private attributes in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a private attribute named __value in the class.

Python

class MyClass:
    def __init__(self, val):
        self.[1] = val

Drag options to blanks, or click blank then click option'

Avalue

B__value

C_value

Dval

Attempts:

3 left

💡 Hint

Common Mistakes

Using a single underscore instead of double underscores.

Not using underscores at all.

Using the parameter name directly as attribute.

Private attributes in Python start with double underscores, like __value.

2fill in blank

medium

Complete the code to access the private attribute __value inside the class method.

Python

class MyClass:
    def __init__(self, val):
        self.__value = val
    def get_value(self):
        return self.[1]

Drag options to blanks, or click blank then click option'

A__value

B_value

Cvalue

Dval

Attempts:

3 left

💡 Hint

Common Mistakes

Using a single underscore instead of double underscores.

Trying to access the attribute without underscores.

Inside the class, you access private attributes with their exact name, including double underscores.

3fill in blank

hard

Fix the error in accessing the private attribute from outside the class.

Python

obj = MyClass(10)
print(obj.[1])

Drag options to blanks, or click blank then click option'

A__value

Bvalue

C_MyClass__value

D_value

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to access the attribute with just double underscores.

Using the attribute name without underscores.

Private attributes are name-mangled. To access them outside, use _ClassName__attr syntax.

4fill in blank

hard

Fill both blanks to create a private attribute and a method to access it.

Python

class Data:
    def __init__(self, val):
        self.[1] = val
    def get_val(self):
        return self.[2]

Drag options to blanks, or click blank then click option'

A__secret

Bsecret

D_secret

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for attribute and access.

Using single underscore instead of double.

Private attributes use double underscores. Both attribute and access inside class use the same name.

5fill in blank

hard

Fill all three blanks to define a private attribute, a getter method, and access the private attribute outside the class using name mangling.

Python

class Secret:
    def __init__(self, val):
        self.[1] = val
    def get(self):
        return self.[2]

obj = Secret(42)
print(obj.[3])

Drag options to blanks, or click blank then click option'

A__data

C_Secret__data

D_data

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to access private attribute outside class with just double underscores.

Using inconsistent attribute names.

Private attribute uses double underscores. Inside class, access with same name. Outside, use name mangling with _ClassName prefix.

Practice

1. What is the main purpose of using private attributes (starting with __) in a Python class?

easy

A. To speed up the program execution

B. To hide the attribute from outside the class and protect it

C. To make the attribute accessible everywhere

D. To make the attribute a global variable

Solution

1. Step 1: Understand private attribute naming

   Private attributes start with double underscores to hide them from outside access.

2. Step 2: Purpose of hiding attributes

   This protects the data inside the object from accidental or unauthorized changes.

3. Final Answer:

   To hide the attribute from outside the class and protect it -> Option B

4. Quick Check:

   Private attributes = data protection [OK]

Hint: Private attributes start with __ to hide data inside class [OK]

Common Mistakes:

• Thinking private means accessible everywhere
• Confusing private with global variables
• Believing private speeds up code

2. Which of the following is the correct way to define a private attribute named age in a Python class?

easy

A. self.___age

B. self.age

C. self._age

D. self.__age

Solution

1. Step 1: Identify private attribute syntax

   Private attributes start with exactly two underscores, like __age.

2. Step 2: Check options

   self.__age uses self.__age, which is correct. self.age is public, self._age is protected (single underscore), self.___age has three underscores which is invalid.

3. Final Answer:

   self.__age -> Option D

4. Quick Check:

   Private attribute = double underscore [OK]

Hint: Private attribute = double underscore before name [OK]

Common Mistakes:

• Using single underscore instead of double
• Adding too many underscores
• Forgetting underscores

3. What will be the output of this code?

class Person:
    def __init__(self, name):
        self.__name = name
    def get_name(self):
        return self.__name

p = Person('Anna')
print(p.get_name())
print(p.__name)

medium

A. Anna\nAnna

B. AttributeError\nAnna

C. Anna\nAttributeError

D. AttributeError\nAttributeError

Solution

1. Step 1: Understand private attribute access

   The attribute __name is private and cannot be accessed directly outside the class.

2. Step 2: Check print statements

   Calling p.get_name() returns 'Anna' correctly. But p.__name causes AttributeError because it's private.

3. Final Answer:

   Anna\nAttributeError -> Option C

4. Quick Check:

   Private attribute direct access = AttributeError [OK]

Hint: Private attributes cause error if accessed directly outside class [OK]

Common Mistakes:

• Expecting direct access to private attribute
• Ignoring AttributeError on private access
• Confusing method call with attribute access

4. Find the error in this code and fix it:

class Car:
    def __init__(self, model):
        self.__model = model

c = Car('Tesla')
print(c.__model)

medium

A. Add a method inside class to return __model

B. No error, code runs fine

C. Remove underscores from __model

D. Change __model to _model to fix access

Solution

1. Step 1: Identify the error

   Accessing c.__model outside the class causes AttributeError because __model is private.

2. Step 2: Fix by adding a getter method

   Adding a method inside the class to return self.__model allows safe access.

3. Final Answer:

   Add a method inside class to return __model -> Option A

4. Quick Check:

   Private attribute access needs class method [OK]

Hint: Use class method to access private attributes outside class [OK]

Common Mistakes:

• Trying to access private attribute directly
• Removing underscores breaks privacy
• Ignoring need for getter method

5. You want to store a private attribute __balance in a BankAccount class and allow safe updating only through a method that adds money. Which code snippet correctly implements this?

hard

A. class BankAccount:
def __init__(self):
self.__balance = 0
def add_money(self, amount):
self.__balance += amount
def get_balance(self):
return self.__balance

B. class BankAccount:
def __init__(self):
self._balance = 0
def add_money(self, amount):
self._balance += amount
def get_balance(self):
return self._balance

C. class BankAccount:
def __init__(self):
self.balance = 0
def add_money(self, amount):
self.balance += amount
def get_balance(self):
return self.balance

D. class BankAccount:
def __init__(self):
self.__balance = 0
def add_money(self, amount):
self.balance += amount
def get_balance(self):
return self.__balance

Solution

1. Step 1: Check private attribute usage

   class BankAccount: def __init__(self): self.__balance = 0 def add_money(self, amount): self.__balance += amount def get_balance(self): return self.__balance uses self.__balance consistently and privately.

2. Step 2: Verify method updates and access

   The add_money method safely updates __balance, and get_balance returns it correctly.

3. Final Answer:

   The code using self.__balance consistently in all methods -> Option A

4. Quick Check:

   Private attribute updated only inside class methods [OK]

Hint: Update private attributes only via class methods [OK]

Common Mistakes:

• Updating private attribute outside class
• Mixing private and public attribute names
• Not providing method to access private data