How to call a function in Python – Step By Step Guide

Introduction – How to call a function in Python

One of the fundamental aspects of Python programming is calling functions. Functions are blocks of organized, reusable code designed to perform specific tasks. Learning how to call functions in Python is essential for every aspiring programmer.

Learn how to call a function in Python effectively. This comprehensive guide covers various methods and best practices for invoking functions in Python, providing insights from experienced developers and credible sources.

How to Call a Function in Python

Using Parentheses with Function Name

One of the most common and straightforward ways to call a function in Python is by using parentheses with the function name. This method is suitable for functions that do not require any arguments.


# Define a simple function
def greet():
    print("Hello, Python enthusiast!")

# Call the function


Hello, Python enthusiast!

Passing Arguments to Functions

When arguments are passed to functions, their power increases. Arguments give the function the ability to receive input data, which makes it flexible and dynamic. Positional and keyword arguments can be passed to functions in Python.

Positional Arguments
Depending on where they are in the function call, positional parameters are passed. Since the arguments are translated to the respective parameters in the function specification, the order of the arguments counts.


# Define a function with positional arguments
def greet_user(username):
    print(f"Hello, {username}!")

# Call the function with an argument


Hello, John!

Keyword Arguments

You can define which keyword argument relates to which parameter in the function specification by passing a parameter name along with the argument. This approach makes code easier to read, particularly when working with functions that take several arguments.


# Define a function with keyword arguments
def greet_user(greeting, username):
    print(f"{greeting}, {username}!")

# Call the function with keyword arguments
greet_user(greeting="Hi", username="Jane")


Hi, Jane!

Utilizing Default Parameter Values

You can specify default values for function parameter values in Python. The default values specified in the function declaration are used when the function is called without any parameters. When you wish to give your function calls flexibility, this functionality is helpful.


# Define a function with default parameter value
def greet_user(username="Guest"):
    print(f"Hello, {username}!")

# Call the function without an argument


Hello, Guest!

Using the Return Statement

Functions can return values after performing their tasks. To capture and utilize the returned values, you can assign them to variables.


# Define a function with a return statement
def add_numbers(a, b):
    return a + b

# Call the function and store the result
result = add_numbers(3, 5)
print("The sum is:", result)


The sum is: 8

How to Call a Function in Python with Different Scenarios

Calling Functions within the Same Module

When the function you want to call exists within the same module as your current code, you can directly call it by its name.


# Module:

def greet():
    print("Hello from my_module!")

# Calling the function from another part of the code


Hello from my_module!

Invoking Functions from Another Module

To call a function that resides in a different module, you need to import the module first and then use the function name with the module’s namespace.


# Module:

def greet():
    print("Hello from my_module!")

# Module:

import my_module

# Calling the function from the imported module


Hello from my_module!

Calling Built-in Functions

Python provides numerous built-in functions that are readily available for use without the need for importing modules.


# Using built-in functions

# Calculate the absolute value
abs_value = abs(-10)
print("Absolute value:", abs_value)

# Find the maximum value in a list
numbers = [10, 25, 8, 43, 17]
max_value = max(numbers)
print("Maximum value:", max_value)


Absolute value: 10
Maximum value: 43

Calling Functions from External Libraries

External libraries considerably expand Python’s capabilities. You must first install the external library using a package manager like pip before importing the necessary modules or functions in order to call functions from the library.


# Using functions from the "requests" library to fetch data from a URL

import requests

response = requests.get("")
print("Status Code:", response.status_code)


Status Code: 200

Leveraging Lambda Functions

Lambda functions are brief, single-line functions without names, also referred to as anonymous functions. They are helpful when a quick, disposable function is required for a particular purpose.


# Using a lambda function to add two numbers

add = lambda a, b: a + b
result = add(3, 5)
print("The sum is:", result)


The sum is: 8

How to Call a Function in Python Dynamically

Using the 'eval()' Function

The 'eval()' function in Python allows you to evaluate and execute dynamically created Python expressions.


# Using eval() to call a function dynamically

def greet():
    print("Hello from greet() function!")

function_name = "greet"
eval(function_name + "()")


Hello from greet() function!

Using the 'exec()' Function

Similar to 'eval()', the exec() function enables you to execute dynamically generated Python code, including function calls.


# Using exec() to call a function dynamically

def greet():
    print("Hello from greet() function!")

function_name = "greet"
exec(function_name + "()")


Hello from greet() function!

Also Read: Python Operators Guide – Types and Use Cases

Best Practices for Calling Functions in Python

1. Avoid Using 'eval()' and 'exec()'

Although 'eval()' and 'exec()' offer dynamic capabilities, they can introduce security vulnerabilities and are generally discouraged unless absolutely necessary.

2. Choose Descriptive Function Names

Your code will be easier to comprehend and function calls will be clearer if you choose names for your functions that are meaningful and descriptive.

3. Follow PEP 8 Guidelines

Your code, including function calls, will be consistent and understandable if you follow the PEP 8 guidelines.

4. Document Your Functions

Your functions should have detailed documentation that includes information on their use, parameters, return values, and any exceptions they might cause.

5. Test Your Functions Thoroughly

Before deploying your code to production, perform comprehensive testing of your functions to ensure their correctness and reliability.


1. How can I call a function in Python?

To call a function in Python, use the function’s name followed by parentheses. If the function requires arguments, pass them within the parentheses.

2. Can I call a function from another module in Python?

Yes, you can call a function from another module in Python by first importing the module and then using the function name with the module’s namespace.

3. How do I pass arguments to a Python function?

To pass arguments to a Python function, include the arguments within the parentheses when calling the function. Use either positional or keyword arguments based on your requirements.

4. What is the purpose of lambda functions in Python?

Lambda functions are anonymous functions used for small, simple tasks. They are particularly helpful when you need a throwaway function for a specific task.

5. Is it possible to call a function dynamically in Python?

Yes, you can call a function dynamically in Python using the eval() and exec() functions. However, be cautious as they can introduce security risks.

6. What are some best practices for calling functions in Python?

  • Avoid using eval() and exec().
  • Choose descriptive function names.
  • Follow PEP 8 guidelines.
  • Document your functions thoroughly.
  • Test your functions extensively.

Also Read: Top 7 Use Cases of Python


Learning how to call functions in Python is a fundamental skill that every developer should master. This article covered various techniques for invoking functions, including passing arguments, using default parameter values, and leveraging lambda functions. Additionally, we explored how to call functions from different modules and external libraries. Following best practices ensures clean and maintainable code, making your Python projects more efficient and robust.

Before deploying your code, keep in mind to thoroughly test and document your functions. You may call functions in Python with confidence by using the knowledge you’ve learned from this guide, which will also help you become a better programmer.

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