ይህ ትምህርት ገና ወደ አማርኛ አልተተረጎመም፤ ስለዚህ በእንግሊዝኛ ቀርቧል። የእንግሊዝኛውን ገጽ ክፈቱ

match statements

3 min read

Menus are everywhere: dial a USSD code and press 1 for balance, 2 for airtime, 3 for help. You can already build one with if and elif. In this lesson you'll learn match, a statement made for exactly this job, and one trap in it that looks harmless but catches everything.

From elif to match

Here's a menu written the way you know:

choice = "2"
if choice == "1":
    print("Check balance")
elif choice == "2":
    print("Buy airtime")
elif choice == "3":
    print("Help")
else:
    print("Unknown choice")

Ctrl or Cmd + Enter runs

Every branch compares the same name with a fixed value. match says that once:

choice = "2"
match choice:
    case "1":
        print("Check balance")
    case "2":
        print("Buy airtime")
    case "3":
        print("Help")
    case _:
        print("Unknown choice")

Ctrl or Cmd + Enter runs

match choice: names the value to look at. Each case gives a value it might be, called a patternpatternWhat a case compares against. A value written directly, like "2" or 3, is a literal pattern.. Python tries the cases from the top and runs the first one that matches, just like an elif chain. case _: matches anything, so it catches every other choice, like else. Put it last. Change choice to "7", then to 2 without quotes: the number 2 isn't the text "2", so it falls through to _.

Several values in one case

| inside a case means "or": the case matches any of the values. Predict this.

ውጤቱን ገምቱ

Decide before you look. Guessing wrong is how this sticks.

answer = "N"
match answer:
    case "yes" | "y" | "Y":
        print("Let's go!")
    case "no" | "n" | "N":
        print("Maybe later")
    case _:
        print("Please answer yes or no")

Python prints

Maybe later

"N" is one of the values in the second case, so that case runs. Unlike or in an if, | in a case lists values to compare with: no repeating the name needed.

Remember the or bug from lesson 2.3? | in a case is the version that reads the way you'd hope: each value is compared with answer.

A coffee ceremony has three rounds, abol, tona, and bereka. Given the round number, name the round:

round_number = 2
match round_number:
    case 1:
        print("Abol")
    case 2:
        print("Tona")
    case 3:
        print("Bereka")
    case _:
        print("The ceremony has three rounds")

Ctrl or Cmd + Enter runs

The name that catches everything

A pattern must be a value, like "red" in quotes. A bare name without quotes means something else entirely:

የተለመደ ስህተት

This breaks

colour = "blue"
match colour:
    case red:
        print("Stop")
    case "green":
        print("Go")

Python says

SyntaxError: name capture 'red' makes remaining patterns unreachable

The fix

colour = "blue"
match colour:
    case "red":
        print("Stop")
    case "green":
        print("Go")

case red: doesn't compare with a name called red. It means "match anything, and call it red", so no case after it could ever run. Python refuses the program and says so. Put quotes around text patterns.

_ is the one bare name you should use: it's the "anything else" case.

When to use match, and when not

match shines when a value is one of a few fixed options: menu choices, commands, answers, round numbers. It isn't for ranges. A grade depends on whether a score is at least 85 or at least 70, and a case can't ask "at least". For ranges, use if and elif, as in lesson 2.2.

ጥያቄ

Which job suits match best?

መልመጃ

A command menu

Ask for a command and answer it with match. The balance is 150 birr. For balance, print it; for buy, print that airtime was bought; for help, list the commands; for anything else, say the command is unknown.

Output

Command: balance
Your balance is 150 birr

Your code

balance = 150
command = input("Command: ")
# Answer balance, buy, help, and anything else

Ctrl or Cmd + Enter runs

Input

One answer per line, given to input() in order.

መፍትሄውን አሳይ

This is one way to solve it, not the only one. If yours prints the same thing, it works.

balance = 150
command = input("Command: ")
match command:
    case "balance":
        print(f"Your balance is {balance} birr")
    case "buy":
        print("Airtime bought")
    case "help":
        print("Commands: balance, buy, help")
    case _:
        print(f"Unknown command: {command}")

ዋና ዋና ነጥቦች

match compares one value with several patterns and runs the first case that matches.
"yes" | "y" in a case matches either value; case _: matches anything else and goes last.
A bare name like case red: catches everything; put quotes around text patterns.
Use match for a few fixed options, and if / elif for ranges.