# error: Cython.Distutils.build_ext is not available

- **ID:** `python/setuptools-cython-not-found`
- **Domain:** python
- **Category:** install_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

The package uses Cython to build C extensions, but Cython is not installed in the build environment.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 3.10 | active | — | — |

## Workarounds

1. **** (90% success)
   ```
   In pyproject.toml: [build-system] requires = ["setuptools", "Cython"]
   ```
2. **** (85% success)
   ```
   pip install Cython && pip install --no-build-isolation package
   ```
3. **** (80% success)
   ```
   pip install --only-binary :all: package
   ```

## Dead Ends

- **** — May not be in the isolated build environment. (60% fail)
- **** — Still requires Cython. (90% fail)
- **** — May break the build. (70% fail)