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Match True in python

In JavaScript, using the switch statement, I can do the following code:

switch(true){
    case 1 === 1:
        console.log(1)
        break

    case 1 > 1:
        console.log(2)
        break

    default:
        console.log(3)
        break
}

And it’s going to return 1, since JavaScript switch is comparing true === (1 === 1)

But the same does not happen when I try it with Python Match statement, like as follows:

match True:
    case 1 = 1:
        print(1)

    case 1 > 1:
        print(2)

    case _:
        print(3)

It returns:

File "<stdin>", line 2
    case 1 = 1:
           ^
SyntaxError: invalid syntax

And another error is returned if I try it this way:

Check1 = 1 == 1
Check2 = 1 > 1

match True:
    case Check1:
        print(1)

    case Check2:
        print(2)

    case _:
        print(3)

It returns:

case Check1:
         ^^^^^^
SyntaxError: name capture 'Check1' makes remaining patterns unreachable

What would be the cleanest/fastest way to do many different checks without using a lot of if’s and elif’s?

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Answer

In JavaScript, using the switch statement, I can do the following code

I definitely wouldn’t be using JavaScript as any form of litmus or comparator for python.


If you used 1==1 in your first test case, the below is what both of your test cases are ultimately doing.

match True:
    case True:
        print(1)

    case False: #will never get hit
        print(2)

    case _:     #will never get hit
        print(3)

This is why you get the error for the second version. True will only ever be True, so no other case will ever be hit.

Based on your example, it seems like you are trying to use match/case just to determine the “truthiness” of an expression. Put the expression in the match.

match a==1:
    case True: 
        pass
    case False:
        pass

If you have a lot of expressions, you could do something like the below, although I don’t think this is very good.

a = 2

match (a==1, a>1):
    case (True, False):
        print('equals 1')
    case (False, True):
        print('greater than 1')
    case _:
        print(_)

#OR

match ((a>1) << 1) | (a==1):
    case 1:
        print('equals 1')
    case 2:
        print('greater than 1')
    case _:
        print(_)

cases should be possible results of the match, NOT expressions that attempt to emulate the match. You’re doing it backwards. The below link should tell you pretty much everything that you need to know about match/case, as-well-as provide you with alternatives.

Match/Case Examples and Alternatives

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