Getter and setter methods in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a getter method in Python?

A getter method is a function that retrieves or returns the value of a private attribute in a class. It allows controlled access to the attribute.

beginner

What is a setter method in Python?

A setter method is a function that sets or updates the value of a private attribute in a class. It allows controlled modification of the attribute.

intermediate

Why use getter and setter methods instead of accessing attributes directly?

Getter and setter methods help protect data by controlling how attributes are accessed or changed. They can add checks or rules before allowing changes.

intermediate

How do you define a getter method using @property in Python?

You define a method with the @property decorator above it. This method acts like an attribute when accessed, returning the value you want.

intermediate

How do you define a setter method using @property_name.setter in Python?

You define a method with the @property_name.setter decorator, where property_name matches the getter. This method sets the value with any checks you want.

What does a getter method do?

A Returns the value of an attribute

B Sets the value of an attribute

C Deletes an attribute

D Creates a new attribute

A getter method returns the value of an attribute, allowing controlled access.

Which decorator is used to define a getter method in Python?

A @property

B @get

C @setter

D @attribute

The @property decorator is used to define a getter method.

How do you define a setter method for a property named 'age'?

A @age.property

B @age.setter

C @set.age

D @property.setter

The setter method uses @age.setter where 'age' is the property name.

Why might you use a setter method instead of changing an attribute directly?

A To hide the attribute completely

B To make the code slower

C To add validation before changing the value

D To avoid using classes

Setter methods allow adding checks or validation before changing an attribute.

What happens if you try to set a property without defining a setter method?

A The program crashes immediately

B The value is set normally

C The getter method is called instead

D Python raises an AttributeError

Without a setter, trying to set a property raises an AttributeError.

Explain how getter and setter methods help protect data in a Python class.

Think about how you can check or limit changes to data.

Describe how to create a property with both getter and setter methods using decorators.

Remember the naming must match between getter and setter.

Practice

1. What is the main purpose of getter and setter methods in a Python class?

easy

A. To create new classes dynamically

B. To control access to private attributes safely

C. To execute code asynchronously

D. To delete objects from memory

Solution

1. Step 1: Understand getter and setter roles

   Getter methods retrieve attribute values, and setter methods update them while controlling access.

2. Step 2: Identify their purpose in encapsulation

   They protect private data by allowing controlled reading and writing, preventing direct access.

3. Final Answer:

   To control access to private attributes safely -> Option B

4. Quick Check:

   Getter/setter = control private data [OK]

Hint: Getters and setters manage private data access [OK]

Common Mistakes:

• Thinking they create new classes
• Confusing with asynchronous code
• Assuming they delete objects

2. Which of the following is the correct syntax to define a setter method for attribute age using the @property decorator in Python?

easy

A. @property.setter\ndef set_age(self, value):\n self._age = value

B. @setter.age\ndef age(self, value):\n self._age = value

C. @age.setter\ndef age(self, value):\n self._age = value

D. @age.setter\ndef set_age(self):\n self._age = value

Solution

1. Step 1: Recall setter syntax with @property

   The setter uses @attribute.setter decorator and method name matches the attribute.

2. Step 2: Check method signature

   Setter method takes self and value parameters to set the attribute.

3. Final Answer:

   @age.setter\ndef age(self, value):\n self._age = value -> Option C

4. Quick Check:

   Setter uses @age.setter and method age(self, value) [OK]

Hint: Setter uses @attribute.setter and method named attribute [OK]

Common Mistakes:

• Using wrong decorator like @setter.age
• Method name not matching attribute
• Setter missing value parameter

3. What will be the output of the following code?

class Person:
    def __init__(self, name):
        self._name = name

    @property
    def name(self):
        return self._name

    @name.setter
    def name(self, value):
        self._name = value.upper()

p = Person('alice')
p.name = 'bob'
print(p.name)

medium

A. bob

B. Error

C. alice

D. BOB

Solution

1. Step 1: Understand setter behavior

   Setter converts the assigned value to uppercase before storing it.

2. Step 2: Trace code execution

   Initially name is 'alice', then set to 'bob' which setter changes to 'BOB'. Printing returns 'BOB'.

3. Final Answer:

   BOB -> Option D

4. Quick Check:

   Setter uppercases value, output = BOB [OK]

Hint: Setter modifies value before storing, output reflects change [OK]

Common Mistakes:

• Expecting original lowercase 'bob'
• Thinking print shows initial 'alice'
• Assuming code raises error

4. Identify the error in this code snippet using getter and setter methods:

class Car:
    def __init__(self):
        self._speed = 0

    @property
    def speed(self):
        return self._speed

    @speed.setter
    def speed(self):
        self._speed = 100

c = Car()
c.speed = 50
print(c.speed)

medium

A. Setter method missing value parameter

B. Getter method missing return statement

C. Property decorator used incorrectly

D. No error, code runs fine

Solution

1. Step 1: Check setter method signature

   Setter must accept two parameters: self and value to set the attribute.

2. Step 2: Identify missing parameter

   Current setter only has self, missing value parameter, causing error on assignment.

3. Final Answer:

   Setter method missing value parameter -> Option A

4. Quick Check:

   Setter needs (self, value) parameters [OK]

Hint: Setter must have value parameter besides self [OK]

Common Mistakes:

• Omitting value parameter in setter
• Confusing getter and setter decorators
• Assuming code runs without error

5. You want to create a class Temperature that stores temperature in Celsius internally but allows getting and setting the temperature in Fahrenheit using getter and setter methods. Which code correctly implements this behavior?

hard

A. class Temperature:
def __init__(self, celsius=0):
self._celsius = celsius

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

@fahrenheit.setter
def fahrenheit(self, value):
self._celsius = (value - 32) * 5/9

B. class Temperature:
def __init__(self, fahrenheit=32):
self._fahrenheit = fahrenheit

@property
def celsius(self):
return (self._fahrenheit - 32) * 5/9

@celsius.setter
def celsius(self, value):
self._fahrenheit = (value * 9/5) + 32

C. class Temperature:
def __init__(self, celsius=0):
self.celsius = celsius

@property
def fahrenheit(self):
return (self.celsius * 9/5) + 32

@fahrenheit.setter
def fahrenheit(self, value):
self.celsius = (value - 32) * 5/9

D. class Temperature:
def __init__(self, fahrenheit=32):
self.fahrenheit = fahrenheit

@property
def celsius(self):
return (self.fahrenheit - 32) * 5/9

@celsius.setter
def celsius(self, value):
self.fahrenheit = (value * 9/5) + 32

Solution

1. Step 1: Understand internal storage and interface

   The class stores temperature internally in Celsius (_celsius) but exposes Fahrenheit via getter and setter.

2. Step 2: Check getter and setter calculations

   Getter converts Celsius to Fahrenheit; setter converts Fahrenheit to Celsius and stores it.

3. Step 3: Verify correct use of private attribute and decorators

   class Temperature: def __init__(self, celsius=0): self._celsius = celsius @property def fahrenheit(self): return (self._celsius * 9/5) + 32 @fahrenheit.setter def fahrenheit(self, value): self._celsius = (value - 32) * 5/9 uses _celsius internally and @property/@fahrenheit.setter correctly.

4. Final Answer:

   Option A code correctly implements the behavior -> Option A

5. Quick Check:

   Internal Celsius, getter/setter convert Fahrenheit [OK]

Hint: Store Celsius internally, convert in getter/setter for Fahrenheit [OK]

Common Mistakes:

• Storing Fahrenheit internally instead of Celsius
• Using public attributes without underscore
• Mixing getter/setter names and attributes