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Add ascii_only option to StringConstraints#12907

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Viicos merged 5 commits intopydantic:mainfrom
ai-man-codes:feature/string-ascii-only-constraint
Mar 16, 2026
Merged

Add ascii_only option to StringConstraints#12907
Viicos merged 5 commits intopydantic:mainfrom
ai-man-codes:feature/string-ascii-only-constraint

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@ai-man-codes ai-man-codes commented Mar 10, 2026 •
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feat: add ascii_only constraint to StringConstraints

Change Summary

Implements the ascii_only option for StringConstraints as requested in #12300.

Previously, developers had to use an unintuitive regex pattern to enforce ASCII-only strings:

username: Annotated[str, StringConstraints(pattern=r'^[\x00-\x7F]*$')]

This PR adds a clean boolean flag instead:

username: Annotated[str, StringConstraints(ascii_only=True)]

Changes made:

  • pydantic-core: Added ascii_only field to StrConstrainedValidator, implemented the check using Rust's native .is_ascii() before pattern matching for performance, and registered a new StringNotAscii error type
  • pydantic: Exposed ascii_only parameter in StringConstraints, registered it in _known_annotated_metadata.py, and mapped it to the ASCII regex pattern in JSON Schema output
  • docs: Added string_not_ascii section to validation_errors.md

Related issue number

Fixes #12300

Checklist

  • The pull request title is a good summary of the changes - it will be used in the changelog
  • Unit tests for the changes exist
  • Tests pass on CI
  • Documentation reflects the changes where applicable
  • My PR is ready to review, please add a comment including the phrase "please review" to assign reviewers

Selected Reviewer: @Viicos

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codspeed-hq Bot commented Mar 10, 2026 •
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Merging this PR will improve performance by 5.19%

⚡ 1 improved benchmark
✅ 211 untouched benchmarks

Performance Changes

Benchmark BASE HEAD Efficiency
⚡ test_list_of_strs_json_uncached 441.7 µs 419.9 µs +5.19%

Comparing ai-man-codes:feature/string-ascii-only-constraint (5943840) with main (4b92ae3)

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github-actions Bot commented Mar 10, 2026

Coverage report

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FileStatementsMissingCoverageCoverage
(new stmts)		Lines missing
  pydantic
  types.py
  pydantic/_internal
  _known_annotated_metadata.py
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This report was generated by python-coverage-comment-action

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ai-man-codes commented Mar 10, 2026

@davidolrik what do you think about this implementation, can you please review this PR ? Thank you

Viicos
Viicos requested changes Mar 10, 2026
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Please update the https://docs.pydantic.dev/latest/api/standard_library_types/#strings documentation to reflect the change.

Comment thread pydantic-core/tests/validators/test_string.py
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Please remove

Comment thread tests/test_types.py Outdated
@pydantic-hooky pydantic-hooky Bot added awaiting author revision awaiting changes from the PR author and removed ready for review labels Mar 10, 2026
@pydantic-hooky pydantic-hooky Bot assigned ai-man-codes and unassigned Viicos Mar 10, 2026
@Viicos Viicos changed the title Feature/string ascii only constraint Add ascii_only option to StringConstraints Mar 10, 2026
Viicos
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Comment thread docs/api/standard_library_types.md Outdated
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davidolrik commented Mar 10, 2026

@davidolrik what do you think about this implementation, can you please review this PR ? Thank you

I think you ment to highlight @davidhewitt and not me 😊

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ai-man-codes commented Mar 10, 2026 •
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I think you ment to highlight @davidhewitt and not me 😊

yeah, I wanted to highlight @davidhewitt. Sorry for the misunderstanding.

@pydantic-hooky pydantic-hooky Bot added ready for review and removed awaiting author revision awaiting changes from the PR author labels Mar 10, 2026
@pydantic-hooky pydantic-hooky Bot assigned Viicos and unassigned ai-man-codes Mar 10, 2026
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ai-man-codes commented Mar 14, 2026 •
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@Viicos are there any more changes to be done ?

@Viicos Viicos merged commit fbf9c6e into pydantic:main Mar 16, 2026
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@Viicos Viicos added the needs-blogpost-entry This PR needs to be documented in the release notes blog post label Mar 16, 2026
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@davidhewitt davidhewitt davidhewitt approved these changes

@Viicos Viicos Viicos approved these changes

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Add ascii_only option to StringConstraints

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