Defining Your Own Python Function

Defining and Calling Python Functions

Howard Francis
Howard Francis 27 Lessons 2h 23m basics python
Start Now Rate and Review

A function is a self-contained block of code that encapsulates a specific task or related group of tasks. This course will show you how to define your own Python function. You’ll learn when to divide your program into separate user-defined functions and what tools you’ll need to do this.

You’ll also learn the various ways to pass data into a function when calling it, which allows for different behavior from one invocation to the next.

In this course, you’ll learn:

  • How functions work in Python and why they’re beneficial
  • How to define and call your own Python function
  • Mechanisms for passing arguments to your function
  • Some differences between how to work with functions in Python vs C++
  • How to return data from your function back to the calling environment

This course will be the most helpful for you if you’re already familiar with the fundamental concepts of Python, including basic data types, lists and tuples, dictionaries, the import statement, conditional statements, and for loops.

What’s Included:

Downloadable Resources:

Related Learning Paths:

Start Now

Functions in Python

4 Lessons 14m

  1. 1. Defining and Calling Python Functions (Overview)01:27
  2. 2. Functions in Python02:01
  3. 3. Why Use Functions?04:39
  4. 4. Function Calls and Definitions06:47

Argument Passing

7 Lessons 46m

  1. 1. Positional Arguments08:32
  2. 2. Keyword Arguments04:27
  3. 3. Default Parameters05:03
  4. 4. Mutable Default Parameter Values06:26
  5. 5. Pass-By-Value vs Pass-By-Reference in C++10:29
  6. 6. Pass-By-Value vs Pass-By-Reference in Python07:22
  7. 7. Passing Mutable Objects and Side Effects03:51

The return Statement

3 Lessons 16m

  1. 1. Exiting a Function03:35
  2. 2. Returning Data to the Caller05:57
  3. 3. Avoiding Side Effects07:17

Variable-Length Argument Lists

5 Lessons 22m

  1. 1. Argument Tuple Packing05:44
  2. 2. Argument Tuple Unpacking04:46
  3. 3. Argument Dictionary Packing and Unpacking04:23
  4. 4. Put It All Together02:45
  5. 5. Multiple Unpackings in a Function Call05:20

Keyword-Only and Positional-Only Arguments

3 Lessons 18m

  1. 1. Keyword-Only Arguments08:08
  2. 2. Bare Variable Argument Parameter06:18
  3. 3. Positional-Only Arguments04:27

Docstrings and Function Annotations

5 Lessons 24m

  1. 1. Function Docstrings04:28
  2. 2. Function Annotations07:47
  3. 3. Creating and Modifying Annotations04:48
  4. 4. Enforcing Type Checking05:17
  5. 5. Defining and Calling Python Functions (Summary)01:41
Start Now

About Howard Francis

Howard is an avid Pythonista and records video courses for Real Python. He has been teaching beginning programming at the college level for over 20 years in C++, Java, C#, and most recently Python.

» More about Howard

Each tutorial at Real Python is created by a team of developers so that it meets our high quality standards. The team members who worked on this tutorial are:

Christopher

Sadie

Tappan

John

Joanna

Aldren

Jaya

Related Courses:

The Python return Statement: Usage and Best Practices

Using the Python return Statement Effectively

Python Basics: Functions and Loops

Python Basics Exercises: Functions and Loops

Python Basics: Functions and Loops

Python Basics: Functions and Loops

Participant Comments

Avatar image for silvanog31560

silvanog31560 on Aug. 9, 2021

Thank you for this course, it was great! I am sure that once I get some practice I will come back to review this again!

← Browse All Courses