Function in Python

:dart: Learning Objectives

By the end of this lesson, you will be able to:

• Understand what functions are and why we use them
• Create your own functions with and without parameters
• Use return values to get data from functions
• Call functions with different types of arguments

:information_source: Function is a block of organized and reusable code that performs a specific task. It only runs when you call it.

:package: Why Use Functions?

Functions help programmers simplify the coding process. They create organized, reusable code that can perform specific actions whenever you need them.

:wrench: Types of Functions

Python has two categories of functions:

• Built-in functions - Functions that come with Python (ready to use!)
• User-defined functions - Functions you create yourself

Built-in Functions You Already Know

You've already used many built-in functions:

• print() - Shows output on screen
• input() - Gets input from user
• int() - Converts to integer
• str() - Converts to string

:bulb: Want to explore more built-in functions? Check out: Python Built-in Functions Reference

Creating Your Own Functions

Sometimes you need to customize your own function for specific tasks. That's when you create user-defined functions.

When you create a function, you give it a meaningful name. Then, instead of typing the entire block of code repeatedly, you just type the function name!

:sparkles: Advantages of Functions

• Avoids repetition - Write once, use many times!
• Increases readability - Makes your program easier to understand

:books: Key Terms to Remember

Before using functions, let's learn these important terms:

• Call - Using a function (running it)
• Define - Creating a function using the def keyword
• Parameter - A variable in the function that receives a value
• Argument - The actual value you pass to the function
• Return value - Data that the function sends back using the return keyword

:emoji: Two Important Phases

1️⃣ Define/Create Phase

python

def function_name(parameters):
    # Block of code to execute
    return value  # (optional)

2️⃣ Call Phase

python

function_name(arguments)

Function Syntax

The picture below shows the syntax used to create and call a function.

:emoji: Real-Life Example

Think of a function like a recipe for baking a cake! Here's how it works:

python

def recipe(ingredients):
    mix the ingredients
    add milk
    bake the cake in oven
    return cake

Graphical Representation:

:emoji: What We'll Learn

We'll explore three types of functions:

1. Function with no parameter - Simple functions that don't need input
2. Function with parameter - Functions that accept input values
3. Function with return value - Functions that give back results

1️⃣ Function with No Parameter

The simplest function doesn't need any parameters. You just define it with a name and the code to execute. Then call it without any arguments!

python

def greet():
    print("Hello, world")
greet()

Expected output:

output

Hello, world

note This function always does the same thing every time you call it.

2️⃣ Function with Parameter

Sometimes you need to pass values into a function to get different results. Here's how to create a function with parameters:

def greet(name):
    print("Hello, ", name)
greet("Chong Wei")

Expected output:

Hello, Chong Wei

Setting Default Values

You can give parameters default values. If you don't provide an argument, the function uses the default value! Code:

def greet(name="World"):
    print("Hello, ", name)
greet()

Expected output:

Hello, World

Code:

greet("Sharvin")

Expected output:

Hello, Sharvin

Multiple Parameters

Functions can have two or more parameters:

def greet(name, age):
    print("Hello,", name)
    print("You are", age, "years old")
greet("Chong Wei", "18")

Expected output:

Hello, Chong Wei
You are 18 years old

Using Keyword Arguments

Don't want to remember the parameter order? Use keyword arguments!

def greet(name, age):
    print("Hello,", name)
    print("You are", age, "years old")
greet(age="12", name="Sharvin")

Expected output:

Hello, Sharvin
You are 12 years old

:bulb: Keyword arguments let you specify which parameter gets which value, regardless of order!

3️⃣ Function with Return Value

Sometimes you need to get a value back from a function. Use the return keyword to send data back to your main code!

python

def add(num1, num2):
    return num1 + num2
total = add(2,3)
print(total)

Expected output:

output

5
```note

The return value can be stored in a variable for later use!

:memo: Summary

Functions are powerful tools that:

• Help you organize code into reusable blocks
• Can accept parameters for flexibility
• Can return values for further processing
• Make your programs cleaner and easier to understand

Remember the two phases: Define (create) and Call (use)!

:movie_camera: Video

:emoji: AI Prompt

Code with AI: Try using AI to create and learn about functions and modules.

Prompts:

• "Write a Python function to check if a string is a palindrome."
• "Find a Python module for working with dates and times."

:dart: Practice Time!

Try these exercises to master functions:

1. Create a function that greets a person by name
2. Write a function that calculates the area of a rectangle
3. Make a function that checks if a number is even or odd
4. Build a function that converts temperature from Celsius to Fahrenheit