Instance methods in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define an instance method that returns the name of the person.

Python

class Person:
    def __init__(self, name):
        self.name = name
    def get_name(self):
        return self.[1]

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

Aget_name

BName

Cname

Dself.name

Attempts:

3 left

💡 Hint

Common Mistakes

Writing 'Name' with uppercase N causes attribute error.

Using 'get_name' instead of the attribute name returns the method itself, not the value.

The instance method accesses the instance variable name using self.name. Here, the blank is for the attribute name, so just name is correct.

2fill in blank

medium

Complete the code to call the instance method greet on the object p.

Python

class Person:
    def greet(self):
        return "Hello!"

p = Person()
message = p.[1]()

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

Agreet

BGreet

Cgreet()

Dgreeting

Attempts:

3 left

💡 Hint

Common Mistakes

Including parentheses inside the blank causes syntax error.

Using uppercase 'Greet' causes attribute error.

To call an instance method, use the method name without parentheses inside the attribute access, then add parentheses after. So p.greet() is correct, and the blank is just the method name greet.

3fill in blank

hard

Fix the error in the instance method by completing the blank with the correct parameter name.

Python

class Person:
    def __init__([1], name):
        self.name = name

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

Aperson

Bthis

Ccls

Dself

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'cls' which is for class methods.

Using 'this' which is not a Python keyword.

The first parameter of instance methods must be self to refer to the instance.

4fill in blank

hard

Fill both blanks to create an instance method that returns the person's age plus 5.

Python

class Person:
    def __init__(self, age):
        self.age = age
    def future_age(self):
        return self.[1] [2] 5

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

Aage

B+

C-

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using minus or multiplication operators changes the meaning.

Using wrong attribute names causes errors.

The method returns the current age plus 5, so the attribute age and the plus operator + are needed.

5fill in blank

hard

Fill all three blanks to create a method that returns a greeting with the person's name in uppercase.

Python

class Person:
    def __init__(self, name):
        self.name = name
    def greet(self):
        return f"Hello, [1]!".[2]().[3]()

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

Aself.name

Bupper

Cstrip

Dlower

Attempts:

3 left

💡 Hint

Common Mistakes

Using lower() instead of upper().

Calling methods in wrong order causes unexpected output.

The method returns a greeting with the name in uppercase and stripped of whitespace. So self.name is the name, strip() removes spaces, and upper() converts to uppercase.

Practice

1. What is the purpose of the self parameter in an instance method?

easy

A. It refers to the specific object calling the method.

B. It is used to define a static method.

C. It is a keyword to create a new object.

D. It stores the return value of the method.

Solution

1. Step 1: Understand what self represents

   self is a reference to the current object that calls the method, allowing access to its attributes and other methods.

2. Step 2: Differentiate from other options

   Static methods, object creation, and return values are unrelated concepts, which are not the role of self.

3. Final Answer:

   It refers to the specific object calling the method. -> Option A

4. Quick Check:

   self = current object [OK]

Hint: Remember: self means 'this object' inside methods [OK]

Common Mistakes:

• Thinking self is a keyword, not a parameter
• Confusing self with class or static methods
• Assuming self is optional in instance methods

2. Which of the following is the correct way to define an instance method inside a Python class?

easy

A. def method_name():

B. def method_name(*args):

C. def method_name(cls):

D. def method_name(self):

Solution

1. Step 1: Recall instance method syntax

   Instance methods must have self as the first parameter to access the object's data.

2. Step 2: Check each option

   def method_name(): misses self, def method_name(cls): uses cls which is for class methods, and def method_name(*args): uses a generic parameter which is not standard for instance methods.

3. Final Answer:

   def method_name(self): -> Option D

4. Quick Check:

   Instance method = first param self [OK]

Hint: Instance methods always start with self parameter [OK]

Common Mistakes:

• Omitting self in method definition
• Using cls instead of self for instance methods
• Using no parameters or *args incorrectly

3. What will be the output of this code?

class Dog:
    def __init__(self, name):
        self.name = name
    def bark(self):
        return f"{self.name} says Woof!"

my_dog = Dog('Buddy')
print(my_dog.bark())

medium

A. Woof!

B. Buddy says Woof!

C. my_dog says Woof!

D. Error: missing self parameter

Solution

1. Step 1: Understand object creation and method call

   The object my_dog is created with name 'Buddy'. Calling bark() uses self.name which is 'Buddy'.

2. Step 2: Evaluate the return value

   The method returns the string "Buddy says Woof!" which is printed.

3. Final Answer:

   Buddy says Woof! -> Option B

4. Quick Check:

   Method uses self.name = Buddy [OK]

Hint: Instance methods use self to access object data [OK]

Common Mistakes:

• Ignoring self and expecting just 'Woof!'
• Confusing variable name with object name
• Assuming method returns nothing

4. Find the error in this code:

class Car:
    def __init__(self, model):
        self.model = model
    def show_model():
        print(f"Model: {self.model}")

car = Car('Tesla')
car.show_model()

medium

A. Cannot create object without arguments

B. Wrong attribute name used

C. Missing self parameter in show_model method

D. print statement syntax error

Solution

1. Step 1: Check method definition

   The method show_model is missing the self parameter, so it cannot access instance attributes.

2. Step 2: Understand the error cause

   Calling car.show_model() passes the object automatically, but method lacks self to receive it, causing a TypeError.

3. Final Answer:

   Missing self parameter in show_model method -> Option C

4. Quick Check:

   Instance methods need self parameter [OK]

Hint: Always include self as first parameter in instance methods [OK]

Common Mistakes:

• Forgetting self in method definition
• Trying to access self without parameter
• Confusing class and instance methods

5. You want to create a class Counter that counts how many times its method increment is called on each object separately. Which code correctly implements this behavior?

hard

A. class Counter:
def __init__(self):
self.count = 0
def increment(self):
self.count += 1
def get_count(self):
return self.count

B. class Counter:
count = 0
def increment(self):
Counter.count += 1
def get_count(self):
return Counter.count

C. class Counter:
def __init__(self):
self.count = 0
def increment():
self.count += 1
def get_count(self):
return self.count

D. class Counter:
def __init__(self):
self.count = 0
def increment(self):
count += 1
def get_count(self):
return self.count

Solution

1. Step 1: Understand instance vs class variables

   Instance variables (self.count) ensure each object tracks its own count separately. Methods must accept self and update self.count.

2. Step 2: Eliminate incorrect approaches

   Class variables are shared across all instances. Missing self parameter in methods causes TypeError. Updating a local variable doesn't affect the instance attribute.

3. Final Answer:

   class Counter: def __init__(self): self.count = 0 def increment(self): self.count += 1 def get_count(self): return self.count -> Option A

4. Quick Check:

   Instance variables + self = separate counts [OK]

Hint: Use self.variable for per-object data, not class variables [OK]

Common Mistakes:

• Using class variables for per-object data
• Forgetting self in method parameters
• Incrementing local variables instead of instance attributes