Programming Fundamentals › Programming Basics

Pattern Matching

Branching on the shape of data and destructuring it at the same time.

Also known as: match expression, destructuring match

Pattern matching checks whether a value has a particular shape, and pulls out the parts you need in the same step. Instead of testing a condition and then reading fields by hand, you describe the shape you expect and name the pieces in it.

Python 3.10 and later have a match statement. Here’s a small command parser:

def handle(command):
    match command:
        case ["go", direction]:
            return f"moving {direction}"
        case ["quit"]:
            return "bye"
        case _:
            return "unknown command"

handle(["go", "north"])   # 'moving north'
handle(["quit"])          # 'bye'

The first case matches a two-item list whose first item is "go", and binds the second item to direction. The _ case is a catch-all. Other languages, such as Rust and Scala, have their own forms of pattern matching, and many functional languages rely on it heavily.

The classic mistake is treating a match as a faster if chain. Its main value is clarity: each case says what shape it handles, and destructuring removes a layer of index-checking code. Order matters, because the first case that matches wins, so put specific patterns before general ones. A catch-all placed first will hide every case after it. Also, pattern matching doesn’t replace validating input from outside your program.

Conditionals are the simpler tool for plain true/false checks. Reach for pattern matching when the question is about the structure of the data.