Update StringVar to match Python str behavior (#5417)

[ubaidrmn]

Add missing lstrip and rstrip methods to align with Python's str interface. Update strip method to accept a chars argument, consistent with str.strip. Closes #5417.

All Submissions:

• Have you followed the guidelines stated in CONTRIBUTING.md file?
• Have you checked to ensure there aren't any other open Pull Requests for the desired changed?

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

New Feature Submission:

• Does your submission pass the tests?
• Have you linted your code locally prior to submission?

Changes To Core Features:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your core changes, as applicable?
• Have you successfully ran tests with your changes locally?

[greptile-apps]

Greptile Summary

This PR adds lstrip and rstrip methods to StringVar and updates the existing strip method to accept an optional chars argument, aligning StringVar's string API with Python's built-in str.

• state.js gains three new helpers (pyLstrip, pyRstrip, pyStrip) that use new Set(chars) for character matching and correctly handle multi-code-unit (surrogate-pair) emoji in both forward and backward traversal. When chars is null/undefined they delegate to the native trimStart/trimEnd/trim.
• sequence.py integrates the helpers through the @var_operation decorator; Python None is converted to JS null via LiteralVar.create(None), which the JS helpers test with chars == null before branching.
• Unit and integration tests cover all three methods for the no-arg (whitespace) case, a literal chars string, and a StringVar state variable as chars.

Confidence Score: 5/5

Safe to merge — the change is additive, the JS helpers are correct for well-formed strings, and existing behaviour of the no-arg strip path is preserved.

All three strip variants correctly fall back to native trim* methods when no chars are supplied, and use a Set-based character lookup (not a regex) for the chars path. Surrogate-pair handling in the backward-scan of pyRstrip uses codePointAt(end-2), which correctly identifies two-code-unit code points for well-formed strings. The @var_operation decorator's LiteralVar.create(None) → null serialisation is confirmed by the updated unit tests.

No files require special attention.

Important Files Changed

Filename	Overview
packages/reflex-base/src/reflex_base/.templates/web/utils/state.js	Adds pyLstrip, pyRstrip, pyStrip JS helpers. Uses Set-based character matching (not regex), correct Unicode/surrogate-pair handling in both directions.
packages/reflex-base/src/reflex_base/vars/sequence.py	Adds lstrip/rstrip methods to StringVar and updates strip to accept an optional chars arg; delegates to new JS helpers via @var_operation with proper LiteralVar conversion of None → null.
tests/units/test_var.py	Adds unit assertions for lstrip/rstrip/strip covering both zero-arg (null) and literal-chars paths, plus a StringVar-as-chars path.
tests/integration/test_var_operations.py	Integration tests for all three strip variants with no-arg whitespace, literal chars, and state-var chars; expected values match Python semantics.
packages/reflex-base/news/5417.feature.md	Changelog entry for the new lstrip/rstrip methods and updated strip signature.

_{Reviews (2): Last reviewed commit: "Drop the NoneVar fast path; helpers hand..." | Re-trigger Greptile}

[FarhanAliRaza]

I think the greptile raises some valid points.

[ubaidrmn]

I think the greptile raises some valid points.

Hey @FarhanAliRaza, I agree. The escaping issue should be a straightforward fix. I’m working on a solution for the first point. New to the codebase, so still exploring.

[codspeed-hq]

Merging this PR will not alter performance

✅ 26 untouched benchmarks
⏩ 8 skipped benchmarks¹

---

_{Comparing ubaidrmn:fix-5417 (e223f21) with main (9972800)}

Footnotes

1. 8 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩