Difference between method types in Python - Quick Revision & Key Differences

Recall & Review

beginner

What is an instance method in Python?

An instance method is a function defined inside a class that operates on an instance of the class. It takes <code>self</code> as the first parameter, which refers to the specific object calling the method.

beginner

What is a class method in Python?

A class method is a method that takes the class itself as the first argument, usually named <code>cls</code>. It is marked with the <code>@classmethod</code> decorator and can access or modify class state shared by all instances.

beginner

What is a static method in Python?

A static method is a method inside a class that does not take <code>self</code> or <code>cls</code> as the first parameter. It behaves like a regular function but belongs to the class's namespace. It is marked with the <code>@staticmethod</code> decorator.

intermediate

How do instance, class, and static methods differ in how they are called?

Instance methods are called on objects and receive the object as <code>self</code>. Class methods are called on the class and receive the class as <code>cls</code>. Static methods can be called on the class or instance but do not receive any automatic first argument.

intermediate

Why use a class method instead of an instance method?

Use a class method when you need to access or modify class-level data that is shared across all instances, or when you want to create alternative constructors. Instance methods are for behavior related to individual objects.

Which method type automatically receives the instance as the first argument?

A None of the above

B Class method

C Static method

D Instance method

Instance methods receive the instance (self) automatically when called on an object.

Which decorator is used to define a class method?

A @staticmethod

B @instance

C @classmethod

D @class

The @classmethod decorator marks a method as a class method.

What is true about static methods?

A They receive the class as the first argument

B They do not receive any automatic first argument

C They receive the instance as the first argument

D They can only be called on instances

Static methods behave like regular functions inside the class and do not receive self or cls automatically.

When would you use a class method?

A To access or modify class-level data

B To access or modify instance-specific data

C To create a regular function inside a class

D To override instance methods

Class methods are used to work with class-level data shared by all instances.

Which method type can be called on both the class and its instances?

A Static method

B Class method

C None of the above

D Instance method

Static methods can be called on the class or instances without receiving any automatic argument.

Explain the differences between instance, class, and static methods in Python.

Think about what each method receives as the first parameter and what data it can access.

When should you choose to use a class method over an instance method?

Consider the difference between data that belongs to the whole class versus data that belongs to one object.

Practice

1. Which method type in Python automatically receives the instance as the first argument named self?

easy

A. Instance method

B. Class method

C. Static method

D. Global function

Solution

1. Step 1: Understand method types

   Instance methods receive the instance as the first argument, usually named self.

2. Step 2: Identify method with self

   Class methods receive the class as cls, static methods receive no automatic first argument.

3. Final Answer:

   Instance method -> Option A

4. Quick Check:

   Method with self = Instance method [OK]

Hint: Look for self as first parameter for instance methods [OK]

Common Mistakes:

• Confusing cls with self
• Thinking static methods have self
• Mixing global functions with methods

2. Which decorator is used to define a class method in Python?

easy

A. @classmethod

B. @staticmethod

C. @instance

D. @class

Solution

1. Step 1: Recall Python decorators for methods

   Class methods use the @classmethod decorator to receive the class as the first argument.

2. Step 2: Identify correct decorator

   @staticmethod is for static methods, @instance and @class are invalid decorators.

3. Final Answer:

   @classmethod -> Option A

4. Quick Check:

   Class method decorator = @classmethod [OK]

Hint: Class methods always use @classmethod decorator [OK]

Common Mistakes:

• Using @staticmethod for class methods
• Assuming @instance is a valid decorator
• Confusing decorator names

3. What is the output of this code?

class MyClass:
    @staticmethod
    def greet():
        return 'Hello'

print(MyClass.greet())

medium

A. AttributeError

B. TypeError

C. None

D. 'Hello'

Solution

1. Step 1: Understand static method behavior

   Static methods do not require an instance or class argument and can be called directly on the class.

2. Step 2: Analyze the code output

   The static method greet returns the string 'Hello', so print(MyClass.greet()) outputs 'Hello'.

3. Final Answer:

   'Hello' -> Option D

4. Quick Check:

   Static method call returns 'Hello' [OK]

Hint: Static methods can be called on class without arguments [OK]

Common Mistakes:

• Expecting a TypeError for missing self
• Confusing static with instance method call
• Thinking static methods return None by default

4. Identify the error in this code:

class Example:
    @classmethod
    def show(cls):
        print(cls.value)

Example.show()

medium

A. Missing @staticmethod decorator

B. Method should use 'self' instead of 'cls'

C. Missing class attribute 'value'

D. Syntax error in method definition

Solution

1. Step 1: Check class method usage

   The method show is a class method and tries to print cls.value.

2. Step 2: Verify class attribute existence

   The class Example does not define value, so accessing cls.value causes an AttributeError at runtime.

3. Final Answer:

   Missing class attribute 'value' -> Option C

4. Quick Check:

   Class attribute missing causes error [OK]

Hint: Class methods need class attributes to access via cls [OK]

Common Mistakes:

• Confusing instance and class attributes
• Thinking @staticmethod fixes attribute errors
• Using 'self' in class methods incorrectly

5. You want a method that can be called on the class or instance but does NOT access instance or class data. Which method type should you use?

hard

A. Class method

B. Static method

C. Instance method

D. Property method

Solution

1. Step 1: Understand method access types

   Instance methods access instance data via self, class methods access class data via cls.

2. Step 2: Identify method without data access

   Static methods do not access instance or class data and can be called on both class and instance.

3. Final Answer:

   Static method -> Option B

4. Quick Check:

   No data access = Static method [OK]

Hint: No data access means use static method [OK]

Common Mistakes:

• Choosing instance or class method incorrectly
• Confusing property methods with static methods
• Assuming static methods access class data