Objective

In this unit, we'll explore the match-case statement, a feature that was introduced in Python version 3.10. We'll learn how to use the match-case statement effectively to handle multiple conditions, compare it with if-elif-else statements, and practically apply it in a project.

Understanding match-case Statements

In Python 3.10, a new control flow structure was introduced, the match-case statement. It offers more readable syntax and capabilities beyond the if-elif-else statements. This statement allows us to match patterns within data and execute code accordingly.

def determine_shape(sides):
    match sides:
        case 3:
            shape = "Triangle"
        case 4:
            shape = "Square"
        case _:
            shape = "Polygon"
    return shape

In this example, based on the number of sides, we determine whether the shape is a triangle, square, or another type of polygon. The _ is a wildcard that matches anything, similar to the else in if-elif-else statements.

Using match-case for Multiple Conditions

The match-case statement in Python is designed to be more expressive than the if-elif-else statements and to handle complex condition matching more cleanly. This allows us to perform different actions based on different conditions.

For example, let's assume person is a dictionary with name and age keys. This is a common format when working with JSON data or other structured data types. Now let's create a function to greet the person differently based on their name and age.

def greet(person):
    # Use match-case to check the person's name and age
    match person:
        # Check if the person is Alice and is above 18
        case {"name": "Alice", "age": age} if age > 18:
            print("Hello Alice. You are an adult.")
        # Check if the person is Bob and is 18 or below
        case {"name": "Bob", "age": age} if age <= 18:
            print("Hello Bob. You are a minor.")
        # If neither of the above conditions match, greet as a stranger
        case _:
            print("Hello Stranger")

Here, we are not just checking for equality but also matching patterns in data and using conditions. The match-case statement is inspecting the person dictionary, and based on the name and age properties, it is executing the appropriate case. This can be particularly useful when dealing with complex data structures, where pattern matching can make your code cleaner and easier to understand.

case Blocks

Each case in a match-case statement forms a block that is executed when the case is matched. It is important to note that execution doesn't fall through to the next case as in some other languages with switch statements. Once a case is matched, its block is run, and the match statement is exited.

match-case vs if-elif-else

While match-case and if-elif-else can be used in similar situations, match-case offers more expressive power and conciseness in complex scenarios, especially when dealing with data matching and deconstruction. However, if-elif-else remains more straightforward for simple condition checks.

Project: Draw a Shape Where the Color Is Based on the Number of Sides (Using match-case)

Let's update the Unit 4 project to use match-case statements instead of if-elif-else.

import turtle

# Create a new turtle screen and set its background color
screen = turtle.Screen()
screen.bgcolor("white")

# Initialize a turtle object
t = turtle.Turtle()

# Ask the user for a number of sides
num_sides = int(input("Enter the number of sides for your shape (between 3 and 5): "))

# Use match-case to set the color based on the number of sides
match num_sides:
    case 3:
        t.color("red")
    case 4:
        t.color("blue")
    case 5:
        t.color("green")
    case _:
        print("Invalid input! Please enter a number between 3 and 5.")
        quit()

# Draw the shape
for _ in range(num_sides):
    t.forward(100)
    t.right(360/num_sides)

# Wait until the window is closed
turtle.done()

As you can see, this code is nearly identical to Unit 4. However, here we've replaced the if-elif-else statements with an equivalent match-case statement to set the color of the turtle based on the user's input. If the user inputs a value not between 3 and 5, we terminate the program using quit().

In the next unit, we'll explore how to repeat actions using while and for loops.