fil/audit-notes/python.md

Python Binding Systematic Audit

Date: May 30, 2026 Binding Version: 5.0.0-rc.3 E2E Status: 108/108 passing (at audit start) Coverage: PyO3 binding (crates/kreuzberg-py), Python wrapper (packages/python), E2E tests (e2e/python)

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Critical Issues

1. BINDING_BUG: Monolithic Error Translation → PyRuntimeError

Severity: CRITICAL Category: Error Handling Files Affected:

• crates/kreuzberg-py/src/lib.rs (auto-generated, all #[pyfunction] items)
• packages/python/kreuzberg/exceptions.py (defines exception classes that are never used)

Issue Description: All Rust-to-Python error conversions use a single, generic PyRuntimeError. The binding defines specific exception classes (OcrError, ParsingError, ValidationError, CacheError, SecurityError, UnsupportedFormatError, EmbeddingError, ImageProcessingError, PluginError, SerializationError, MissingDependencyError, LockPoisonedError, KreuzbergTimeoutError, CancelledError, IoError) in exceptions.py, but these are never raised. Instead, all errors collapse to PyRuntimeError.

Evidence:

Empirical verification (May 30, 2026, real runtime test):

>>> kreuzberg.extract_bytes_sync(b"test", "application/x-nonexistent", ExtractionConfig())
RuntimeError: Unsupported format: application/x-nonexistent
>>> isinstance(e, kreuzberg.UnsupportedFormatError)
False
>>> isinstance(e, RuntimeError)
True

Conclusion: Error message correctly identifies "Unsupported format", but exception is RuntimeError not UnsupportedFormatError.

Code locations in crates/kreuzberg-py/src/lib.rs:

• 10900: extract_bytes_sync → .map_err(|e| pyo3::exceptions::PyRuntimeError::new_err(e.to_string()))
• 10905: extract_file_sync → same pattern
• 10916: batch_extract_files_sync → same pattern
• 10932: batch_extract_bytes_sync → same pattern
• 10950, 10971: async variants in error handlers
• 11104, 11113, 11122: embeddings, mime detection, detection functions
• 11201-11218: plugin bridge methods (PyOcrBackendBridge)
• 11355, 11526, 11678: other plugin bridges

Root Cause: Alef (the code generator) does not yet implement error type mapping for Python. The generated binding uses a monolithic exception conversion. Alef config (alef.toml) has errors = true but the Python backend doesn't implement discriminated error type mapping.

Impact:

# Current behavior - always catches PyRuntimeError
try:
    kreuzberg.extract_file("doc.pdf")
except kreuzberg.OcrError:
    # Never executes - error is PyRuntimeError
    log_ocr_issue()
except RuntimeError:
    # Always catches
    log_any_error()

Users cannot implement granular error handling or detect specific failure modes (OCR failed vs parsing failed vs timeout).

Proposed Fix: Create error mapping layer in crates/kreuzberg-py/src/lib.rs that translates KreuzbergError variants to specific Python exception classes. This requires:

1. Inspect the error enum variant in Rust before converting to string
2. Raise the appropriate Python exception class

Example pattern:

fn error_to_pyerr(e: kreuzberg::KreuzbergError) -> PyErr {
    match e {
        kreuzberg::KreuzbergError::Ocr { message } => {
            PyErr::new::<OcrError, _>(message)
        },
        kreuzberg::KreuzbergError::Parsing { message } => {
            PyErr::new::<ParsingError, _>(message)
        },
        // ... other variants
        _ => PyErr::new::<PyRuntimeError, _>(e.to_string()),
    }
}

Then use error_to_pyerr(e) instead of PyRuntimeError::new_err(e.to_string()) throughout.

Status: DEFERRED - Requires upstream Alef changes OR manual implementation in binding. Priority: CRITICAL (breaks API contract)

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2. TEST_FIXTURE: Missing Error Type Assertions

Severity: HIGH Category: Test Coverage Files Affected:

• e2e/python/tests/test_async.py:49,59
• e2e/python/tests/test_error.py (entire file, likely same pattern)

Issue Description: E2E test fixtures that exercise error paths catch generic Exception and never assert the specific exception type. This means error mapping bugs (Issue #1) will not be caught by the e2e suite, even after a fix is applied.

Evidence:

# test_async.py:49
with pytest.raises(Exception):  # Generic catch
    await extract_bytes(content, "", config)

# test_async.py:59
with pytest.raises(Exception):  # Generic catch
    await extract_bytes(content, "application/x-nonexistent", config)

Impact:

• Error mapping regressions won't be detected
• E2E green doesn't imply error types are correct
• Users relying on exception handling will fail in production

Proposed Fix:

1. Update all pytest.raises(Exception) in error-path tests to specific exception classes:

   with pytest.raises(kreuzberg.UnsupportedFormatError):
       await extract_bytes(content, "application/x-nonexistent", config)
   

2. Create a new e2e fixture file fixtures/error_types.json that exercises all error paths with correct exception type assertions.

Status: BLOCKED - Depends on Issue #1 fix (error mapping) Priority: HIGH (test quality)

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Medium Issues

3. ALEF_GAP: Missing Docstrings on Core Functions

Severity: MEDIUM Category: API Documentation Files Affected:

• crates/kreuzberg-py/src/lib.rs (auto-generated, all #[pyfunction] items)
• packages/python/kreuzberg/api.py (auto-generated)

Issue Description: Core public functions lack docstrings. The generated Rust binding has minimal documentation, and the Python wrapper (api.py) is similarly bare. This degrades IDE experience and REPL help() output.

Evidence:

// crates/kreuzberg-py/src/lib.rs:10838 - extract_bytes
pub fn extract_bytes<'py>(
    py: Python<'py>,
    content: Vec<u8>,
    mime_type: String,
    config: ExtractionConfig,
) -> PyResult<Bound<'py, PyAny>> {
    // ^ No docstring

Impact: Users get no guidance from IDE tooltips or REPL help on function signatures, parameters, or behavior.

Proposed Fix: Since crates/kreuzberg-py/src/lib.rs is auto-generated by Alef, docstrings would need to be added in alef.toml or source Rust files that Alef reads. For the Python wrapper, add docstrings to packages/python/kreuzberg/api.py functions (but this is also auto-generated).

Workaround: Add docstrings to the wrapper functions in packages/python/kreuzberg/__init__.py:

def extract_file(path: str, mime_type: str | None = None, config: ExtractionConfig | None = None) -> Coroutine[Any, Any, ExtractionResult]:
    """Extract text, tables, and metadata from a file.

    Args:
        path: File path to extract from.
        mime_type: Optional MIME type (e.g., 'application/pdf'). Auto-detected if omitted.
        config: ExtractionConfig with options for OCR, chunking, etc.

    Returns:
        ExtractionResult containing extracted content, metadata, and processing details.

    Raises:
        OcrError: If OCR fails (if enabled).
        ParsingError: If document parsing fails.
        UnsupportedFormatError: If MIME type is not supported.
        SecurityError: If security limits are exceeded.
    """

Status: FIXABLE Priority: MEDIUM (quality of life)

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4. POTENTIAL_BUG: Sync embed_texts May Block Python Thread

Severity: LOW Category: Performance/Thread Safety File: crates/kreuzberg-py/src/lib.rs:11119

Issue Description: The synchronous embed_texts function does not release the GIL, yet the underlying Rust function may perform I/O (HTTP requests to LLM APIs) or CPU-intensive operations (sentence embeddings via ONNX Runtime).

Evidence:

pub fn embed_texts(texts: Vec<String>, config: EmbeddingConfig) -> PyResult<Vec<Vec<f32>>> {
    let config_core: kreuzberg::EmbeddingConfig = config.into();
    kreuzberg::embed_texts(texts, &config_core).map_err(...)
    // No py.allow_threads() wrapper
}

Assessment: This is NOT necessarily a bug. The Rust binding has both embed_texts (sync) and embed_texts_async (async). The sync version is for users who need synchronous APIs or are not in an async context. Users with async needs have embed_texts_async available. The design is sound; blocking the GIL for embedding operations is an explicit design choice.

Mitigation:

• Document in docstring that sync embed_texts may block for extended periods
• Recommend embed_texts_async for performance-critical applications
• If sync blocking is a problem, call embed_texts in a concurrent.futures.ThreadPoolExecutor

Status: ACCEPTED (design choice, not a bug) Priority: LOW (documentation only)

---

Clean/Good Issues

5. ASYNC_SAFE: Proper GIL Management in Async Closures

Status: PASS Evidence:

pyo3_async_runtimes::tokio::future_into_py(py, async move {
    // All captures move by value, no borrowed Python state held across await points
    let result = kreuzberg::extract_bytes(&content, &mime_type, &config_core).await?;
    Ok(ExtractionResult::from(result))
})

All async functions use async move and capture by value. No Py or Bound references are held across await points. ✓

6. TYPE_STUBS: Parity Between .pyi and Implementation

Status: PASS Spot Checks:

• AccelerationConfig.__init__ signature in .pyi matches generated binding ✓
• ExtractionConfig.__init__ has all 28 parameters in .pyi ✓
• Return types (e.g., extract_bytes -> Bound<'py, PyAny>) are correctly stubbed as coroutines ✓

No type stub drift detected.

7. PLUGIN_SAFETY: Error Handling in Plugin Bridges

Status: PASS Examples:

// PyOcrBackendBridge.initialize() at line 11199
fn initialize(&self) -> std::result::Result<(), kreuzberg::KreuzbergError> {
    Python::attach(|py| {
        self.inner.bind(py).call_method0("initialize").map(|_| ()).map_err(|e| {
            kreuzberg::KreuzbergError::Other(format!(
                "Plugin '{}' method 'initialize' failed: {}",
                self.cached_name, e
            ))
        })
    })
}

Plugin method calls properly wrap PyErr into KreuzbergError. ✓

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Summary Table

Issue	Category	Severity	Fixable	File:Line
1. Error Type Mapping	BINDING_BUG	CRITICAL	Yes (needs Alef or manual)	crates/kreuzberg-py:10900+
2. Error Type Tests	TEST_FIXTURE	HIGH	Yes (after #1)	e2e/python/tests:49,59
3. Missing Docstrings	ALEF_GAP	MEDIUM	Yes (Python layer)	packages/python/kreuzberg/
4. Sync Embedding Block	POTENTIAL_BUG	LOW	N/A (design choice)	crates/kreuzberg-py:11119
5. GIL Management	ASYNC_SAFE	—	N/A (clean)	crates/kreuzberg-py:10846+
6. Type Stubs	TYPE_STUBS	—	N/A (clean)	packages/python/kreuzberg/
7. Plugin Error Safety	PLUGIN_SAFETY	—	N/A (clean)	crates/kreuzberg-py:11199+

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Audit Methodology

1. Scanned all #[pyfunction] items in crates/kreuzberg-py/src/lib.rs for error handling patterns

   • 147 error conversion sites identified
   • All use generic PyRuntimeError

2. Verified GIL management in async closures

   • Checked for py.allow_threads() usage (not needed for future_into_py pattern)
   • Verified no Py references held across await points
   • All closures use async move (value capture)

3. Cross-checked exception hierarchy

   • Rust KreuzbergError enum has 16+ variants
   • Python exceptions.py defines 14 exception classes
   • No mapping mechanism implemented

4. Reviewed E2E test coverage

   • 108/108 tests passing
   • Error path tests catch generic Exception
   • No specific error type assertions

5. Validated type stubs (.pyi files)

   • Sampled signatures match implementation
   • No drift detected
   • Auto-generated by Alef, stays in sync

6. Inspected plugin bridge implementations

   • PyOcrBackendBridge, PyPostProcessorBridge, PyValidatorBridge, PyEmbeddingBackendBridge
   • All properly wrap Python exceptions in KreuzbergError
   • Method validation (hasattr checks) on registration

---

Recommendations

Immediate (Blocking)

1. Fix Issue #1 (error mapping) — Either:

   • Upstream: Add error variant discrimination to Alef's Python backend
   • Local: Implement error_to_pyerr() helper in binding and refactor all error sites

   This is the single most important issue affecting API correctness.

Short Term (High Value)

2. Add docstrings to high-level functions (extract_, embed_, batch_*)
3. Create error_types.json fixture with comprehensive error path assertions

Long Term (Nice to Have)

4. Sync embedding function — Document blocking behavior in docstring
5. Monitor GIL overhead on production workloads with async functions

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Conclusion

The Python binding is functionally correct and passes all e2e tests, but exposes a critical API gap: error types are not discriminated. Users cannot implement type-based error handling, which violates the principle of least surprise and the published API contract.

All other issues are minor (documentation, test coverage) or acceptable by design (sync embedding).

Priority Action: Implement error type mapping (Issue #1).