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This has to do with the new Python 3.10 beta and the new match syntax. Is there any way to check if a pattern is simply contained in an iterable? the most obvious solution, to simply put two wildcards on either side, but that raises a SyntaxError due to the unpacking syntax coming from iterable unpacking.

Is there any possible way to do this? NOTE: the use of things like wrapper classes around numbers in the example would be fine, as long as it works using the match blocks and is at least somewhat readable, but I have already tried this somewhat and not had much success

example:

numbers = [1, 2, 3, 5, 7, 8, 9] #does not have to be a list, could be a class if needed

match numbers:
    # this just raises a SyntaxError, but I need a way to do something equivalent to this
    case [*_, (5 | 6), *_]:
        print("match!")
Drdilyor
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tjf801
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1 Answers1

5

No, we don't currently have any plans to support iterable containment checks as part of the structural pattern matching syntax.

The best way to rewrite your example in legal Python is with a normal if test:

if any(i in (5, 6) for i in numbers):
    print("match!")

If the containment check is just one part of a more complex pattern, you can write it as a guard instead:

match something:
    case [pattern, capturing, numbers] if any(i in (5, 6) for i in numbers):
        print("match!")

Of course, if you have a sequence, it is also possible to find an item at a known index:

match numbers:
    case [_, _, _, 5 | 6, *_]:
        print("match at position 3!")
    case [*_, 5 | 6, _, _, _]:
        print("match at position -4!")

With that said...

the use of things like wrapper classes around numbers in the example would be fine, as long as it works using the match blocks and is at least somewhat readable

...I suppose mapping patterns could be hacked to make this work (provided that all of your items are hashable and don't have unusual equality rules):

match dict.fromkeys(numbers):
    case {5: _} | {6: _}:
        print("match!")

I strongly recommend the if form over this, though.

Brandt Bucher
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