Structural Pattern Matching (match-case / PEP 634)

1Concept

Python 3.10 introduced Structural Pattern Matching with `match` and `case`. It allows matching on values, destructuring sequences (`[x, y, *rest]`), mappings (`{'status': s}`), and class instances (`Point(x, y)`), with guard clauses (`if condition`).

2Architecture Diagram

match command.split():
  case ["go", ("north" | "south" | "east" | "west") as direction]:
  case ["get", item]:
  case _:

3Code Example

def process_api_response(response):
    match response:
        case {"status": 200, "data": list() as items} if len(items) > 0:
            return f"Success: Processed {len(items)} items"
        case {"status": 200, "data": []}:
            return "Warning: Empty dataset returned"
        case {"status": 404, "error": message}:
            return f"Not Found Error: {message}"
        case {"status": code}:
            return f"HTTP Status Code: {code}"
        case _:
            return "Malformed Response Payload"

print(process_api_response({"status": 200, "data": ["User1", "User2"]}))
print(process_api_response({"status": 404, "error": "User ID missing"}))

4Expected Output

Success: Processed 2 items
Not Found Error: User ID missing

5Key Takeaways

• ✓`_` serves as the wildcard pattern matching anything without binding variable names.
• ✓Guard clauses (`if condition`) run only after the pattern structure successfully matches.
• ✓Mapping patterns match even if the dictionary contains additional extra keys.