Fix pydantic constraint rendering

[koxudaxi]

Summary by CodeRabbit

• New Features

  • Deterministic, robust Python-literal rendering for defaults, constraints, and generated field arguments; preserves special floats, tuples, and stable set ordering.
  • Improved numeric-constraint normalization for integer-safe handling and Decimal-aware type hints.
  • Safer regex literal handling for generated patterns.

• Bug Fixes

  • Regex patterns with escaped quotes now produce valid, importable code.
  • Non-finite numeric defaults (inf/NaN) render as valid Python expressions.

• Tests

  • Added integration tests for regex handling, integer-constraint safety, and non-finite value rendering.

[coderabbitai]

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📝 Walkthrough

Walkthrough

Centralizes safe Python literal rendering (PythonCode, represent_python_value) and Fraction-based integer-constraint normalization, integrates them into base and Pydantic field/type generation (including regex literal validation), and adds integration tests plus updated expected generated outputs.

Changes

Python value representation and constraint handling

Layer / File(s)	Summary
Core value representation and constraint normalization utilities src/datamodel_code_generator/python_literal.py, src/datamodel_code_generator/types.py	Adds PythonCode and represent_python_value() for deterministic rendering of Python literals and special floats; adds normalize_integer_constraint(s) using Fraction, updates DataType.type_hint to render callable kwargs with represent_python_value(), and enables Decimal import detection.
Base field default representation src/datamodel_code_generator/model/base.py, src/datamodel_code_generator/model/__init__.py	DataModelFieldBase.represented_default now uses represent_python_value() for default rendering; UNDEFINED import adjusted.
Pydantic base field constraints and defaults src/datamodel_code_generator/model/pydantic_base.py	Adds _INTEGER_CONSTRAINTS, replaces strict-constraint helper with _get_strict_field_constraint() that normalizes/casts integer-vs-float constraint values, and renders Field(...) kwargs and defaults using represent_python_value().
Pydantic v2 type-specific constraints src/datamodel_code_generator/model/pydantic_v2/types.py	Adds _get_regex_literal() validated via ast, uses normalize_integer_constraints() in get_data_int_type(), and routes pattern constraints through the regex literal helper; hostname pattern mapping updated.
Integration tests for generated code rendering tests/main/test_main_general.py	Adds helpers to generate/import Pydantic v2 code and three integration tests covering escaped-quote regex patterns, integer constraints from decimals, and non-finite numeric defaults rendering/evaluation.
Updated expected generated outputs tests/data/expected/...	Expected outputs updated to use Decimal('...') for condecimal constraints and inline float('...') for special float defaults/constraints.

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Possibly related PRs

• koxudaxi/datamodel-code-generator#3022: Related rework around pydantic base/constraint rendering and DataModelField surface.

Suggested labels

breaking-change-analyzed

Suggested reviewers

• ilovelinux

Poem

A rabbit trims the Python lines,
I stitch raw code with tidy rhyme,
Fractions keep constraints aligned,
Regex literals checked in time,
Tests clap paws — the models shine! 🐰

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 75.76% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Fix pydantic constraint rendering' directly and clearly describes the main objective of the pull request, which involves fixing how Pydantic field constraints and defaults are rendered in generated code.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix-pydantic-constraint-rendering

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[github-actions]

📚 Docs Preview: https://pr-3289.datamodel-code-generator.pages.dev

[codspeed-hq]

Merging this PR will degrade performance by 11.78%

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

❌ 5 regressed benchmarks
✅ 6 untouched benchmarks
⏩ 98 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	WallTime	test_perf_all_options_enabled	5.1 s	5.8 s	-12.37%
❌	WallTime	test_perf_openapi_large	2.6 s	3 s	-12.11%
❌	WallTime	test_perf_complex_refs	1.9 s	2.1 s	-11.85%
❌	WallTime	test_perf_kubernetes_style_pydantic_v2	2.4 s	2.7 s	-11.44%
❌	WallTime	test_perf_aws_style_openapi_pydantic_v2	1.7 s	1.9 s	-11.14%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing fix-pydantic-constraint-rendering (c336673) with main (9fa06c7)}

Footnotes

1. 98 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. ↩

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (9fa06c7) to head (c336673).

Additional details and impacted files

@@            Coverage Diff             @@
##              main     #3289    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files          115       116     +1     
  Lines        26017     26173   +156     
  Branches      3284      3310    +26     
==========================================
+ Hits         26017     26173   +156     

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

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[github-actions]

Breaking Change Analysis

Result: Breaking changes detected

Reasoning: This PR changes generated code output in multiple ways: (1) non-finite floats use float() calls instead of math imports, (2) decimal constraints use Decimal() objects, (3) integer fractional constraints are normalized, (4) msgspec now renders array length constraints that were previously ignored, and (5) msgspec required nullable fields no longer get default None. The msgspec.jinja2 template also changed its default rendering condition. These are breaking changes because users regenerating models will see different output, and the msgspec nullable field change alters the runtime constructor signature of generated Struct classes.

Content for Release Notes

Code Generation Changes

• Non-finite float values now use float() calls instead of math imports - Generated code previously rendered inf, -inf, and nan (with from math import inf, nan). Now renders float('inf'), float('-inf'), and float('nan') without the math import. Semantically equivalent but changes generated output. (Fix pydantic constraint rendering #3289)
• Decimal constraint arguments now use Decimal() objects - condecimal() constraints previously used bare int/float values (e.g., condecimal(ge=0, le=1000)). Now uses Decimal objects (e.g., condecimal(ge=Decimal('0'), le=Decimal('1000'))) with an added from decimal import Decimal import in generated code. (Fix pydantic constraint rendering #3289)
• Integer fields with fractional constraints are normalized to integer-safe bounds - Fractional constraint values on integer types are now converted: gt: 0.5 becomes ge: 1, lt: 2.5 becomes le: 2, and multiple_of: 1 is dropped entirely. Previously these fractional values were passed through as-is to conint() or Field(). (Fix pydantic constraint rendering #3289)
• msgspec array length constraints are now rendered - min_items and max_items schema constraints on array fields are now emitted as Meta(min_length=..., max_length=...) annotations in msgspec output. Previously these constraints were silently ignored. (Fix pydantic constraint rendering #3289)
• msgspec required nullable fields no longer get default = None - Required nullable fields in msgspec Structs previously received a = None default assignment. Now they are rendered without a default, requiring callers to provide the value explicitly. (Fix pydantic constraint rendering #3289)

Custom Template Update Required

• msgspec.jinja2 template default value condition changed - The condition for rendering default value assignments changed from not field.required or field.use_default_with_required or field.data_type.is_optional or field.nullable to not field.required or field.use_default_with_required. Custom templates derived from the built-in msgspec template may need to be updated. (Fix pydantic constraint rendering #3289)

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This analysis was performed by Claude Code Action

[github-actions]

🎉 Released in 0.62.0

This PR is now available in the latest release. See the release notes for details.