fix: Specify Python str semantics for character classification functions - #177
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mwiebe wants to merge 2 commits into
Open
fix: Specify Python str semantics for character classification functions#177mwiebe wants to merge 2 commits into
mwiebe wants to merge 2 commits into
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The isdigit/isalpha/isalnum/isspace/isupper/islower descriptions in RFC
0006 and the 2026-02 Expression Language spec did not say which
character-class convention applies, and implementations diverged:
openjd-rs used Rust char predicates, making isdigit ASCII-only while
isalnum was Unicode-wide, so isdigit('\u0663') and isalnum('\u0663')
disagreed (openjd-rs issue #309).
Clarify that these functions have exactly the semantics of the Python
str methods of the same name over the Unicode Character Database,
document the cased-character rule for isupper/islower and the
isalnum-vs-isalpha/isdigit relationship, and add a conformance test
covering Unicode inputs where the conventions differ.
Signed-off-by: Mark <399551+mwiebe@users.noreply.github.com>
Follow-up to the character classification clarification: the title and capitalize descriptions had the same ambiguity, and implementations diverged the same way (word boundaries by alphanumeric-ness instead of cased-ness, uppercase instead of titlecase mappings, no Final_Sigma context rule). Clarify both function rows and the section note in RFC 0006 and the 2026-02 Expression Language spec, and extend the Unicode conformance test with title/capitalize cases covering digit word boundaries, titlecase digraph mappings, sharp-s expansion, and final sigma. Signed-off-by: Mark <399551+mwiebe@users.noreply.github.com>
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fix: Specify Python str semantics for character classification functions
Description of the change. What is being added or fixed?
RFC 0006 and the 2026-02 Expression Language spec describe
isdigit,isalpha,isalnum,isspace,isupper, andislowerwith one-linesummaries ("True if all characters are digits...") that don't say which
character-class convention applies. Every language draws different lines
through Unicode — Rust's
Alphabeticproperty is a superset of Python'sL*categories, Rust has no notion ofNumeric_Type, and so on — soimplementations diverged: openjd-rs used Rust's
charpredicates, whichmade
isdigitASCII-only whileisalnumwas Unicode-wide, and the twocontradicted each other for characters like
'٣'(U+0663 ARABIC-INDICDIGIT THREE). Reported as
openjd-rs#309.
This PR:
exactly the semantics of the Python
strmethods of the same name overthe Unicode Character Database, with the specific Unicode properties named
per function.
isalnumis strictly broader thanisalpha OR isdigit(Numeric_Type=Numeric characters like½), and thecased-character rule for
isupper/islower(uncased characters areignored; titlecase characters are cased but neither upper nor lower).
implementations aren't broken by UCD updates.
expr2.2.4--string-classification-unicode) with21 assertions on characters where the conventions differ, using
\uXXXXescapes so the file stays ASCII. The test fails against openjd-rs
mainand passes against the fix in the companion PR.
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