B15 - match

sources: python docs, ArjanCodes

• compares a given expression with successive patterns in the case block(s)
• several literals can be combined using pipes (|)

def run_command(command: str) -> None:
    match command:
        case "quit":
            print("quitting")
            quit()
        case "help":
            print("getting help")
        case other:
            print(f"unknown command: {other!r}")

def run_command_2(command: str) -> None:
    match command.split():
        case ["load", filename]:
            print(f"loading {filename}")
        case ["save", filename]:
            print(f"saving {filename}")
        case ["quit" | "exit" | "bye"]:
            print("quitting")
            quit()
        case other:
            print(f"unknown command: {other!r}")

• if other is not used in the case, it can be replaced with _

...
case _:
	print("unknown command")

case ["quit" | "exit" | "bye", "--force"]:
	print("quitting")

• here, "--force" needs to be added to the string to quit

case ["quit" | "exit" | "bye", *rest]:
	if "--force" in rest or "-f" in rest:
		print("force quitting")
	else:
		print("quitting")

case ["quit" | "exit" | "bye", *rest] if "--force" in rest or "-f" in rest:
	print("force quitting")
	quit()
case ["quit" | "exit" | "bye"]:
	print("quitting")
	quit()

• patterns can look like unpacking assignments
• they can be used to bind variables

# point is an (x, y) tuple
match point:
    case (0, 0):
        print("origin")
    case (0, y):
        print(f"y={y}")
    case (x, 0):
        print(f"x={x}")
    case (x, y):
        print(f"X={x}, Y={y}")
    case _:
        raise ValueError("Not a point")

• the second and the third patterns combine a literal and a variable

• the variable binds a value from the subject

• classes can be used as well

from dataclasses import dataclass     
from typing import list     
import shlex


@dataclass
class Command:
    """class that represents a command"""
    
    command: str
    arguments: list[str]


def run_command_4(command: Command) -> None:
    match command:
        case Command(command = "load", arguments = [filename]):
            print(f"loading {filename}")
        case Command(command = "save", arguments = [filename]):
            print(f"saving {filename}")
        case Command(command = "quit" | "exit" | "bye", arguments = ["--force" | "-f"]):
            print("force quitting")
            quit()
        case Command(command = "quit" | "exit" | "bye"):
            print("quitting")
            quit()
        case _:
            print(f"Unknown command: {command!r}")
       
    
def main() -> None:
    while True:
        command, arguments = shlex.split(input("Enter command: "))
        run_command_4(Command(command, arguments))

• note: the order of the cases matter
  • if the quit case is placed before quit -f, it will take precedent and entering quit if will simply quit