Pattern Matching (match/case)

Introduction

Introduced in Python 3.10, match/case provides powerful structural pattern matching — like a switch statement on steroids.

Basic Syntax

value = 2

match value:
    case 1:
        print("One")
    case 2:
        print("Two")
    case 3:
        print("Three")
    case _:
        print("Other")  # _ is wildcard (default)

Matching Against Literals

command = "quit"

match command:
    case "quit" | "exit" | "q":
        print("Exiting...")
    case "help" | "?":
        print("Available commands: ...")
    case "save":
        print("Saving...")
    case _:
        print(f"Unknown command: {command}")

Matching Against Objects

def process_point(point):
    match point:
        case (0, 0):
            print("Origin")
        case (0, y):
            print(f"Y-axis at y={y}")
        case (x, 0):
            print(f"X-axis at x={x}")
        case (x, y):
            print(f"Point at ({x}, {y})")
        case _:
            print("Not a point")

Matching with Guards

def categorize_number(n):
    match n:
        case x if x < 0:
            print("Negative")
        case 0:
            print("Zero")
        case x if x % 2 == 0:
            print(f"Positive even: {x}")
        case _:
            print(f"Positive odd: {n}")

Matching Class Instances

from dataclasses import dataclass

@dataclass
class Rectangle:
    width: float
    height: float

@dataclass
class Circle:
    radius: float

def area(shape):
    match shape:
        case Rectangle(width=w, height=h):
            return w * h
        case Circle(radius=r):
            return 3.14159 * r ** 2
        case _:
            raise ValueError("Unknown shape")

Best Practices

Always include a case _: default to handle unexpected values
Use guards when you need additional conditions beyond the pattern
Match against classes for clean polymorphic behavior
Don’t overuse match — simple if/elif is often more readable for simple checks

Practice Exercises

Exercise 1: Write a match statement that categorizes HTTP status codes (1xx, 2xx, 3xx, 4xx, 5xx).

Exercise 2: Create a simple expression evaluator using match on nested tuples like (‘add’, (‘num’, 1), (‘num’, 2)).