gh-138864: Improve SyntaxError message for case with expression
#138865
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terryjreedy
reviewed
Sep 13, 2025
ilovelinux
reviewed
Sep 15, 2025
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Nope, sorry :) |
Misc/NEWS.d/next/Core_and_Builtins/2025-09-13-12-51-34.gh-issue-138864.Otm5li.rst
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| | a="case" patterns guard? ':' NEWLINE !INDENT { | ||
| RAISE_INDENTATION_ERROR("expected an indented block after 'case' statement on line %d", a->lineno) } | ||
| invalid_case_pattern: | ||
| | "case" a=expression guard? ':' block { |
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Maybe it would be better to use this variant?
"case" a=expression 'as'? expression? guard? ':' block
For cases like this:
match ...:
case T[1] as E:
print(1)
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This will be slower and a bit more unreadable I think and also allows to match "case" a=expression 'as' guard ':' block which makes no sense.
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We can run for ('as' expression)?. But "slower" sounds ugly, maybe such a little change doesn't worth it.
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In my opinion this makes already awesome python error messages (thanks, @pablogsal!) even cooler.
Maybe there are some hidden things that I've missed? I would be happy to fix them :)
In case this complicates our parser quite a bit - feel free to close.
case ...:generates unclearSyntaxErrormessage #138864