Python Class and Function: How to call a function in the same class

Depending on the use case, there are a couple of ways you can use to call a function in the same class in Python.

The different ways are:

1. Using the getattr() function
2. Using the self keyword
3. Using the class name and the @classmethod decorator
4. Using the class name and the @staticmethod decorator
5. Using the super() function to call a method from the pa

When considering the efficiency of each method, the article provides a couple of ways that I have used to call a function in the same class in Python. Besides, I have outlined the best approach to use based on the maintainability, readability, and organization of the code.

Before I show you, in detail, the different methods you can use to call a function within the same class in Python, we need to understand classes and functions in Python. Otherwise, you may jump right into the different ways.

Understanding classes and functions in Python

Having a strong understanding of classes and functions is important because the majority of the code that you will write will be organized in chunks.

These chunks are commonly classes and functions that allow you to write reusable and maintainable code.

Together, they form the backbone of Python programming practices such as object-oriented programming.

What is a function in Python?

A function in Python is a block of code that is used to perform a particular task by taking in some inputs, manipulating the inputs, and returning an output. As functions perform only one thing, they are very useful when creating reusable chunks of code that can be used across different areas of your code.

By organizing a couple of lines of code that perform a particular task into a function, you can reuse these lines without having to repeat all the lines. You only need to call the function by mentioning the name of the function followed by two parentheses. Here is an example of how you would call a function called my_function: my_function().

An example of a function that takes in some parameters or inputs is this:

def greet(name):
    greeting = f"Hello {name}"
    print(greeting)

Here, the function, greet(), takes in the name of the user, manipulates it to add some greeting text, and displays the result to the user containing the salutation and the name of the user.

Here’s how you would call such a function

greet('Steve')

Creating functions in Python is very simple.

How to create a function in Python

Here are the steps to take to create a function in Python:

Step 1: Identify the use case of the function (what is the function going to do?)

Before you start defining a function in Python, first identify what the function is going to achieve.

Besides, know what inputs the function will receive, the processing it is going to do, and the output it will produce.

Once you have a clear understanding of the use case of the function, you will have a pretty clear and describable name for the function.

With that, you can name the function according to the tasks it will be intended for.

Step 2: Write the keyword def followed by the function name and parentheses.

Open your favorite code editor. On a new or existing Python file, create a function by following these actionable steps:

Write the keyword def

def

Define the function name after the keyword def

def my_function

Add parentheses after the function name

def my_function()

If you want the function to receive some inputs, add parameter name or names inside the parentheses:

def my_function(parameter1, parameter2)

After the parentheses, add a colon at the end

def my_function(parameter1, parameter2):

Press Enter to jump to a new line. Indent the new line with four spaces.

Step 3: Write the code that performs the task inside the function

After the indentation, write the code that manipulates the inputs to produce the outputs achieving the objectives of the function.

def my_function(parameter1, parameter2):
    # write the processing here
    area_of_a_square = parameter1 * parameter2

Step 4: Define how you want to present the outputs

You can instruct the function to present the outputs through a print statement or the return keyword. With a print statement, the output will be displayed on the Terminal.

With a return keyword, you can use the result in another area of your code or in another function to perform extra processing.

To use a print statement, here’s how the print keyword is used in Python:

def my_function(parameter1, parameter2):
    # write the processing here
    area_of_a_square = parameter1 * parameter2

    # write how the processed results will be displayed here
    print(area_of_a_square)

The same for a return keyword

def my_function(parameter1, parameter2):
    # write the processing here
    area_of_a_square = parameter1 * parameter2

    # write how the processed results will be displayed here
    print(area_of_a_square)

Step 5: Call the function while providing the necessary input parameters

If you used the print keyword, you can explicitly call the function. Calling the function will print the output on the Terminal.

my_function(2, 2)

4 should be printed on the Terminal.

In the case where you may have used the return keyword, you should store the output in a variable so as to use it later in your code.

Here’s how you would do that:

result = my_function(2, 2)

# you can print it later
print(result)

Creating and calling functions in Python is as easy as that.

Now, let’s look at Python classes.

What is a class in Python?

A class in Python is the blueprint for creating objects that have attributes and methods (functions declared within a class).

Objects are also known as instances.

In a class, attributes are the variables that store data while the methods are the functions that perform actions.

For example, a class for a Person might have attributes such as height, weight, age, etc. Also, the Person class can have methods that include walking(), tasting(), running(), etc, of which are definable actions that a person can perform.

Whenever you create objects of the Person class, each person object can have its own attributes and methods. person_a can have different attributes and perform actions that are different from person_b.

However, these attributes and methods, whether performed or possessed by any of the objects, must first be declared in a class.

How to create a class in Python

Here are the steps to take to create a class in Python:

Step 1: Identify the class’s use case (what object will the class represent?)

Before you start defining a class in Python, first identify what the class is going to represent in the real world.

Besides, know what attributes and methods the class will have depending on the properties and actions performed by the objects.

Once you understand the use case of the class, you will have a pretty clear and descriptive class name, attributes, and method names.

Step 2: Write the keyword class followed by the class name and a colon at the end.

Open your favorite code editor. On a new or existing Python file, create a class by following these actionable steps:

Write the keyword class

class

Define the class name after the keyword class. In Python, you should name your classes starting with a capital letter.

Also, give the class name a descriptive name. Do not use numbers as actual class names, either.

class Person

Add a colon after the class name.

class Person:

Press Enter to jump to a new line. Indent the new line with four spaces.

class Person:
    ...

After indentation, start by defining the attributes of the class. Attributes are declared inside a magic method called __init__.

class Person:
    # start with attributes
    def __init__(self, first_name, age):
        self.first_name = first_name
        self.age = age
        
   

Note the additional parameters in the magic method __init__, first_name and age. These are called constructors. They are used to initialize the object attributes that are supplied during object creation.

Just the same way we did with our function example prior, you can do the same with a class when creating every object.

When it comes to creating the object, you should pass the input parameters that are unique to every object that you instantiate.

Remember to add a new line and indent with four spaces. Just as we did with a regular function prior.

Step 3: Write the methods that perform the tasks

After declaring the attributes, define the class methods. Class methods are the functions that perform actions that are related to the object.

In our example, a person object can have methods such as walk() and talk().

These methods are defined inside the Person class using the function declaration syntax.

class Person:
    # start with attributes
    def __init__(self, first_name, age):
        self.first_name = first_name
        self.age = age
        
    # declare the methods after the attributes
    def walk(self):
       print("Oy! I can walk. I am walking, mate")
       
      
    def talk(self):
       print("Oy!")

Step 4: Create objects using the class name followed by parentheses and input parameters

To create an object in Python, follow these steps:

Write the class name followed by parentheses

Person()

If you have input parameters, add them inside the parentheses.

Note that I have written only the input parameters without writing the keyword self.

Person("Stephen", 23)

Instantiate the object by assigning it to a variable

person1 = Person("Stephen", 23)

The code above creates an instance of the Person class and is assigned to the variable, person.

Step 5: Access attributes and methods of the object by using the dot notation

After instantiating the object, you can access the attributes and methods of an object by using the dot.

With the example of the person1 object, you can get the first name by using person1.first_name.

print(person1.first_name)


# output
Stephen

Besides, you can access the class methods (or actions performed by the object) in a similar way.

To access the walk action of the Person object, here’s how you would do that:

person1.walk()

# results
Oy! I can walk. I am walking, mate

Creating objects from declared classes is as easy as that.

It is not only easy but also helps organize your code; bundle together data and behavior unique to some entities; and create modular code.

How classes and functions are used together in Python

Classes and functions are used together in Python to create more complex code that interacts together to achieve an overall program objective.

Such complexity is achieved through interaction that happens between a class and a function either by

1. Functions being used in classes (Functions, known as methods, can be defined inside a class)
2. Functions invoking classes to create objects (Classes being used inside functions)

With that brief introduction to classes and functions, let’s see the different ways to call a function within the same class in Python.

Different ways to call a function within the same class in Python

Python provides a number of approaches to use to call a function within the same class that includes:

1. Using the self keyword
2. Using the getattr() function
3. Using the class name and the @classmethod decorator
4. Using the class name and the @staticmethod decorator
5. Using the super() function to call a method from the parent class. Using inheritance to call a function from the parent class within a child class.

How to call a function within the same class using the self keyword

Follow these actionable steps to call a function within the same class using the self keyword:

Actionable Step 1: Define the function you want to call inside the class

If you wish to call a function, it must exist within the class you call it from.

For example, if you have a class called Jedi and you want to call a function probably called use_the_force(), then you should make sure you have created a method called use_the_force.

Remember, a function declared inside the class is called a method

class Jedi:
    def __init__(self, moniker, lightsaber_color):
        self.moniker = moniker
        self.lightsaber_color = lightsaber_color
        self.force_points = 100
    
    

Create the method you wish to call

class Jedi:
    def __init__(self, moniker, lightsaber_color):
        self.moniker = moniker
        self.lightsaber_color = lightsaber_color
        self.force_points = 100
    
    # here is the method we will call
    def use_the_force(self):
        if self.force_points > 0:
            print(f"{self.moniker} is using the force.")
            self.force_points -= 10
        else:
            print(f"{self.moniker} has no more force points.")

Actionable Step 2: Inside another method, call the function using self.method_name() syntax

Following the Jedi example above, here’s a new method that calls the previously created function, use_the_force

    def duel(self, opponent):
        print(f"{self.moniker} is dueling with {opponent}.")
        self.use_the_force()
        print(f"{self.force_points} force points remaining")
        

Your class should look like this:

class Jedi:
    def __init__(self, moniker, lightsaber_color):
        self.moniker = moniker
        self.lightsaber_color = lightsaber_color
        self.force_points = 100
    

    def use_the_force(self):
        if self.force_points > 0:
            print(f"{self.moniker} is using the force.")
            self.force_points -= 10
        else:
            print(f"{self.moniker} has no more force points.")

    # new method that will call another methow within this class
    def duel(self, opponent):
        print(f"{self.moniker} is dueling with {opponent}.")

        # calling another function within the same class
        self.use_the_force()
        print(f"{self.force_points} force points remaining")
        

And that’s how you can call a function within the class in Python. After creating an object and calling the duel() function, the called function, use_the_force() will be invoked too.

master_luke = Jedi('Luke', 'Green')
master_luke.duel('Kylo Ren')


# results
Luke is dueling with Kylo Ren.
Luke is using the force.
90 force points remaining

Let’s see other ways to call a function within the same class.

How to call a function within the same class using the getattr() function

Follow these steps to call a function within the same class using the getattr() function:

First, import the function, getattr from builtins module using Python import syntax.

from builtins import getattr

Second, pass the name of the method you wish to call inside a string like this:

getattr(self, 'name_of_the_function_to_call')()

Here’s an example:

from builtins import getattr


class MyClass:
    def first_function(self):
        print("first function called")
    
    def second_function(self):
        print("second function called")
        
        # call the method using getattr()
        getattr(self, 'first_function')()

Create an object and call the function that invokes the first function.

#create an object
obj = MyClass()

#call second function
obj.second_function()


# result
second function called
first function called

How to call a function within the same class using class name and the @classmethod decorator

You can also call a function within a class using the @classmethod decorator. Here’s how you do it:

Add the @classmethod decorator to the class you wish to call

class MyClass:
    @classmethod    # add the @classmethod decorator you wish to call
    def first_function(cls):
        print("first function called")

Then call the decorated method in another method using the syntax: ClassName.function_to_call()

class MyClass:
    @classmethod
    def first_function(cls):
        print("first function called")

    def second_function(self):
        print("second function called")

        # call the function like this
        MyClass.first_function()

And here’s how you access the function that calls another function in a class:

#call second function
MyClass().second_function()

How to call a function within the same class using class name and the @staticmethod decorator

You can also call a function within a class using the @staticmethod decorator. Here’s how you do it:

Add the @staticmethod decorator to the class you wish to call

class MyClass:
    @staticmethod    # add the @staticmethod decorator you wish to call
    def first_function(cls):
        print("first function called")

Then call the decorated method in another method using the syntax: ClassName.function_to_call()

class MyClass:
    @staticmethod    # add the @staticmethod decorator you wish to call
    def first_function():
        print("first function called")

    def second_function(self):
        print("second function called")

        # call the function like this
        MyClass.first_function()

And here’s how you access the function that calls another function in a class:

#call second function
MyClass().second_function()

How to call a function using the super() function from the parent class within a child class.

Another way to call a function within the same class is where you use inheritance.

You can call a function from the parent class within the child class using the super() function that gives you access to the parent class methods.

Here are the steps to take to inherit functions from a parent class into a child class:

Step 1: Create the parent class with the method you wish to call:

class Parent:
    def first_function(self):
        print("The first function is called")

Step 2: Create the child class and the method that calls the parent’s class method

class ChildClass(Parent):
     # Code for the method that call a parent's class method
     def second_function(self):
         print("The second function is called")
         
         # use the super() function to call the parent class method
         super().first_function()

Step 3: Create an object of the child class and call the function invoking the parent’s method

#create an object of child class
obj = ChildClass()

#call second function
obj.second_function()

In the example above, when the second_function method is called, it will print its print statement, “The second function is called” and then invoke the first_function method of the parent class printing, “The first function is called”

The second function is called
The first function is called

The recommended approach for calling functions within a class

The recommended approach to calling a function within a class in Python is to use the self keyword within the same class. It makes the code readable, organized, and easy to understand.

When dealing with parent and child classes, the best way to call a function from the parent class is to use super().method_to_call() syntax. It is also clean and organized.

Tips for optimizing function calls in Python (with the recommended approach

1. Avoid using global variables. They can slow down the function execution or lead to incorrect inputs when other functions manipulate the variables.
2. If you wish to access the attributes and methods of an object, consider using the getattr() function to call methods.
3. Use inheritance to reuse methods defined in the parent class. It not only helps you achieve code reusability but also allows you to produce maintainable code.

Related Question

Can we have two methods in a class with the same name in Python?

It is possible to have two or more methods in a class with the same name. Method overloading is the term used to refer to multiple methods having the same name in a Python class. However, this is not a recommended practice for writing Python code because it makes code less readable, hard to debug, and hard to understand.

Python does not support method overloading by default.

Here is an example of an overloaded method in Python:

class MyClass:
    def similar(self, x, y=0):
        return x + y

    def similar(self, x, y=0, z=0):
        return x + y + z
 

With this implementation, the second method will overwrite the first method. Python only uses the latest declared method. Therefore, the similar method will take 3 three arguments instead of two.

Note: Method overloading in Python where two methods use the same name can lead to unexpected behavior and bugs in your code.

Conclusion

In conclusion, calling a function within the same class in Python can be achieved in several ways that include:

1. Using the self keyword, class name, and the dot (.) notation,
2. Using @classmethod and @staticmethod decorators,
3. Using the getattr() function, and
4. Using inheritance where the super() function is used to access parent methods and properties.

With all these approaches, the self keyword is considered to be the most readable, maintainable, modular, and organized way of calling a function within a class.