Python · Functions
Intro to Functions
The full text of this chapter, to read or revisit. To practise, do the exercises.
▶ Do the exercisesExercise 1 — What are Functions?
Imagine you're training multiple Codémon and need to display a welcome message for each one. Without functions, you'd have to write the same code over and over:
print("============================")
print("Welcome to Codémon Training!")
print("============================")
print("Training Aquachu...")
print("============================")
print("Welcome to Codémon Training!")
print("============================")
print("Training Pyrochu...")
print("============================")
print("Welcome to Codémon Training!")
print("============================")
print("Training Florachu...")
This is repetitive and hard to maintain. What if you want to change the message? You'd have to update it in multiple places!
Functions solve this problem by letting you write code once and reuse it many times. This follows the DRY principle: Don't Repeat Yourself.
Why Functions Matter
Functions help you:
- Write less code
- Make your code easier to read
- Fix bugs in one place instead of many
- Organize your code better
Exercise 2 — Creating Your First Function
In Python, we create functions using the
def
keyword (short for "define"). Here's the basic syntax:
def function_name():
# Code to execute goes here
# This code is indented
Let's break this down:
-
def
tells Python we're creating a function
-
function_name
is what we call our function (you choose this!)
-
()
are parentheses (required, even if empty for now)
-
:
marks the end of the function header
- The code inside must be indented (usually 2 or 4 spaces)
def show_welcome():
print("============================")
print("Welcome to Codémon Training!")
print("============================")
# To use the function, we "call" it:
show_welcome()
Notice how we:
1. Define the function with
def show_welcome():
2. Call the function with
show_welcome()
The function doesn't run until we call it!
Common Mistakes
- Forgetting the colon
:
after the function name
- Not indenting the code inside the function
- Forgetting the parentheses
()
when calling the function
- Last but not least, forgetting to call the function!
Exercise 3 — Identifying Valid Function Syntax
Which of the following is the correct way to define a function in Python?
Options
• def greet_codemon():
print("Hello, Codémon!")
• def greet_codemon()
print("Hello, Codémon!")
• def greet_codemon:
print("Hello, Codémon!")
• function greet_codemon():
print("Hello, Codémon!")
Hint : Remember: functions need the ```def``` keyword, parentheses ```()```, a colon ```:```, and indented code inside.
Exercise 4 — Function Parts and Their Names
Match each part of a function with its correct name:
Items to match
• def
• show_message
• ()
• :
Definitions
• Keyword to create a function
• Function name
• Parentheses (required after function name)
• Colon (marks end of function header)
Exercise 5 — Complete the Function Definition
Complete the code to define a function that displays a training message:
____ train_codemon________
print("Training your Codémon...")
print("Great job!")
train_codemon()
Options: def function : ; ()
Hint : Remember the basic syntax: ```def function_name():``` followed by indented code.
Exercise 6 — Understanding Function Calls
What happens when you define a function in Python?
def say_hello():
print("Hello!")
Options
• Nothing is printed - the function is just stored in memory
• "Hello!" is printed immediately
• An error occurs
• The function runs automatically every time the program starts
Hint : Defining a function doesn't run it. You need to call it with ```function_name()``` to execute the code inside.
Exercise 7 — Create a Complete Function
Complete this code to create and call a function that displays a Codémon's power level:
____ show_power()____
print("Codémon power: 75")
# call the function
____
Options: def function : ; show_power() show_power call show_power()
Hint : First define the function with ```def```, then call it using the function name with parentheses.
Exercise 8 — Calling Functions Multiple Times
The real power of functions is that you can call them as many times as you want! Let's see this in action:
def battle_cry():
print("⚡ Codémon, attack! ⚡")
# Call it three times
battle_cry()
battle_cry()
battle_cry()
See how we wrote the code once but used it three times? This is much better than copying and pasting the same code (especially with real code and big functions)!
You can call a function anywhere in your code after it's been defined, and as many times as you need.
Function Naming Convention
Function names should:
- Use lowercase letters
- Use underscores between words (snake_case)
- Be descriptive of what the function does
- Examples:
calculate_damage()
,
heal_codemon()
,
show_stats()
Exercise 9 — Identify the Correct Code
Which code correctly defines and calls a function that displays "Codémon healed!"?
Options
• def heal():
print("Codémon healed!")
heal()
• def heal()
print("Codémon healed!")
heal()
• def heal():
print("Codémon healed!")
heal()
• def heal():
print("Codémon healed!")
heal
Hint : Check for: colon after function definition, proper indentation, and parentheses when calling.
Exercise 10 — Fix the Broken Function
This code has several errors. Fix them to make the function work correctly:
____ display_stats()____
print("Name: Aquachu")
print("Type: Water")
# Call the function
____
Options: def function : ; display_stats() display_stats
Hint : Remember: ```def``` keyword, colon, proper indentation for both lines, and parentheses when calling.
Exercise 11 — Codémon Battle Simulator
Create a battle simulator using a function and a loop! Your tasks:
1. Print "=== Battle Started ==="
2. Define a function
fight()
that prints "⚔️ Aquachu attacks!"
3. Use a loop to call
fight()
5 times (simulate 5 attacks)
4. Print "=== Victory! ==="
Starter code
# 1. Print battle start message
# 2. Define fight() function
# 3. Loop 5 times and call fight() each time
# 4. Print victory message