How to Call a Function in Python: A Beginner’s Step-by-Step Guide (2026)

Learning how to call a function in Python is essential for writing efficient and organized code. Functions are blocks of code that only run when they are called, making them a fundamental building block in Python programming. Instead of writing the same code repeatedly for different inputs, you can create functions to reuse code over and over again.

When you’re new to Python, understanding what a function is and how to call it properly can significantly improve your code’s readability and functionality. In fact, a function can return data as a result and helps you avoid code repetition, which is particularly valuable as your programs grow more complex. 

Throughout this beginner-friendly guide, you’ll learn the step-by-step process of defining and calling a function in Python, common mistakes to avoid, and practical examples to strengthen your understanding. Let’s begin!

What is a Function in Python?

A function in Python is essentially a reusable block of code designed to perform a specific task. Think of it as a mini-program within your program that you can call whenever needed. Functions follow the principle of “write once, use many times,” making your code more organized and efficient.

In programming terms, a function is a named block of code that takes input, processes it, and often returns an output. Moreover, Python treats functions as first-class objects, meaning they can be assigned to variables, passed to other functions, and returned as values.

The primary purpose of functions is to enable abstraction in your code. This means you can call a function with the required arguments without worrying about how it works internally. This concept is fundamental to writing clean, maintainable Python code.

Functions offer several key advantages:

• Code reusability – Instead of writing the same code repeatedly for different inputs, you can create a function once and reuse it multiple times
• Better organization – Functions help divide your program into smaller, manageable chunks
• Easier maintenance – When you need to update how something works, you only need to change it in one place
• Improved readability – Well-named functions make your code self-documenting and easier to understand

Python comes with numerous built-in functions that are always available, but you can also create your own custom functions (known as user-defined functions). These user-defined functions allow you to extend Python’s capabilities to match your specific needs.

Functions can be simple or complex depending on your requirements. A basic function might just print a message, whereas a more sophisticated one might perform complex calculations or data transformations.

Understanding what functions are is the first step. Next, you’ll need to learn how to define and call them properly. Though a function only runs when it is called, it must first be defined with the proper syntax. Additionally, functions can take optional parameters and may or may not return values.

The concept of functions is universal across programming languages, but Python’s implementation is particularly elegant and straightforward, making it ideal for beginners to learn.

How to Define a Function in Python

To create your own functions in Python, you need to understand the proper definition syntax. Before you can call a function, you must first define it properly. Let’s explore how to define functions step by step.

1) Syntax of a Function

The general syntax for defining a function in Python follows this structure:

def function_name([parameters]):

    # function body – code block

    # statements to execute

    [return expression]  # optional

A Python function definition consists of several key components:

1. The def keyword that starts the function definition
2. A valid function name (identifier)
3. Optional parameters in parentheses
4. A colon to end the function header
5. An indented code block (the function body)
6. An optional return statement

2) Using the def Keyword

The def keyword is fundamental to creating functions in Python. This keyword tells Python that you’re about to define a new function. Consider this example:

def greet(name):

    return f”Hello, {name}!”

Here, def creates a function named greet() that accepts one argument, name. When called with greet(“Alice”), it returns the string “Hello, Alice!”.

The power of the def keyword is that it allows you to encapsulate logic that can be executed whenever needed simply by calling the function’s name with parentheses.

3) Indentation Rules

Unlike many other programming languages that use braces, Python relies on indentation to define code blocks. For function definitions, indentation is crucial:

• Standard practice is to use 4 spaces per indentation level
• All code within the function body must be indented consistently
• PEP 8 (Python’s style guide) recommends 4 spaces rather than tabs

For example:

def calculate_area(length, width):

    area = length * width

    return area

If your function accepts multiple parameters that make the line too long, you can format it in several accepted ways:

# Add 4 spaces to distinguish arguments clearly

def long_function_name(

    var_one, var_two, var_three, var_four):

    print(var_one)

Proper indentation not only makes your code work correctly but furthermore enhances readability for yourself and others who might review your code.

How to Call a Function in Python

Once you’ve defined a function in Python, actually using it requires a function call. Calling a function tells Python to execute the code inside that function. Let’s explore how to do this correctly.

1) Basic Function Call Syntax

Calling a function in Python is straightforward – simply type the function’s name followed by parentheses. These parentheses are mandatory even when the function takes no arguments:

def hello_world():

    print(“Hello, world!”)

hello_world()  # Calls the function

Always remember that forgetting the parentheses will reference the function as an object instead of executing it. This distinction is critical for beginners to understand.

2) Calling With Arguments

Functions often require information to work with, which you provide as arguments within the parentheses. There are two main ways to pass arguments:

Positional arguments must match the order defined in the function:

def greet(name, age):

    print(f”Hello {name}, you are {age} years old.”)

greet(“Rahul”, 25)  # Output: Hello Rahul, you are 25 years old.

Keyword arguments explicitly name each parameter, allowing for any order:

greet(age=25, name=”Rahul”)  # Same output as above

Indeed, you can mix both styles, yet positional arguments must come first:

greet(“Rahul”, age=25)  # Valid

3) Calling Multiple Times

One of the primary advantages of functions is reusability. You can call the same function repeatedly with different inputs:

def my_function():

    print(“Hello from a function”)

my_function()

my_function()

my_function()  # Function executes three times

This ability makes functions extremely powerful for repetitive tasks, saving you from duplicating code.

4) Calling Functions With Return Values

Many functions produce output using the return statement. To capture and use this output:

def get_greeting():

    return “Hello from a function”

# Store the return value in a variable

message = get_greeting()

print(message)

# Or use the return value directly

print(get_greeting())

During function execution, after the return statement is reached, the function stops running and sends the value back to the caller. Subsequently, you can use this value in any expression where it makes logical sense.

Functions without a return statement automatically return None. Therefore, it’s important to capture return values only from functions designed to provide them.

Common Mistakes When Calling Functions

Even experienced Python programmers occasionally make mistakes when calling functions. Being aware of these common errors will help you troubleshoot your code faster while learning how to call a function in Python properly.

1) Forgetting Parentheses

One of the most frequent mistakes when calling functions is omitting parentheses. In Python, parentheses are essential when invoking functions:

def greet():

    return “Hello, World!”

greeting = greet  # Without parentheses

print(greeting)   # Outputs: <function greet at 0x00000123456789>

greeting = greet()  # With parentheses

print(greeting)     # Outputs: Hello, World!

Without parentheses, Python returns a reference to the function object itself rather than executing it. This distinction is crucial as it completely changes the behavior of your code.

2) Wrong Number of Arguments

Python requires functions to be called with the correct number of arguments. If your function expects two arguments but receives only one, you’ll get a TypeError:

def my_function(fname, lname):

    print(fname + ” ” + lname)

my_function(“Emil”)  # Error: missing required argument

Python raises this error to prevent unpredictable behavior in your code. Generally, you must match the expected parameter count unless your function uses default values or variable argument lists.

3) Case Sensitivity in Function Names

Python is case-sensitive, meaning myFunction() and MyFunction() are considered completely different functions:

def myFunction():

    return “Hello, Python!”

print(myFunction())   # Works correctly

print(Myfunction())   # NameError: name ‘Myfunction’ is not defined

This sensitivity applies to all identifiers in Python, including function names. Typically, Python functions use lowercase with underscores for readability (e.g., calculate_total()).

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Concluding Thoughts…

Mastering Python functions marks a significant milestone in your programming journey. Throughout this guide, you’ve learned that functions are more than just blocks of code—they serve as essential building blocks that make your programs more efficient and organized. Therefore, understanding how to define and call functions properly will drastically improve your coding experience.

As you continue practicing with Python functions, you’ll develop an intuitive understanding of when and how to use them effectively. Before long, you’ll find yourself naturally breaking down problems into function-sized chunks—a hallmark of proficient Python programmers.

Now that you understand the fundamentals of defining and calling functions in Python, you’re well-equipped to write more elegant and efficient code. Take this knowledge and apply it to your own projects, and you’ll quickly see how these principles transform your approach to programming.

FAQs

Q1. How do I call a function in Python? 

To call a function in Python, write the function name followed by parentheses. If the function requires arguments, place them inside the parentheses, separated by commas.

Q2. What happens if I forget the parentheses when calling a function? 

If you forget the parentheses when calling a function, Python will treat it as a reference to the function object itself rather than executing the function. This is a common mistake that can lead to unexpected behavior in your code.

Q3. Can I call a function multiple times in my program? 

Yes, you can call a function multiple times in your program. This is one of the main advantages of functions, as they allow you to reuse code without having to write it repeatedly.

Q4. How do I capture the return value of a function? 

To capture the return value of a function, assign the function call to a variable. For example: result = my_function(). You can then use this variable to access the value returned by the function.

Q5. What’s the difference between positional and keyword arguments when calling a function?

Positional arguments are passed to a function based on their order, while keyword arguments are explicitly named. For example, func(1, 2) uses positional arguments, while func(a=1, b=2) uses keyword arguments. Keyword arguments provide more flexibility and clarity, especially for functions with many parameters.