# error: subprocess-exited-with-error

× python setup.py bdist_wheel did not run successfully.
│ exit code: 1
╰─> [12 lines of output]
    ModuleNotFoundError: No module named 'Cython'

- **ID:** `python/pip-error-subprocess-exited-with-error`
- **Domain:** python
- **Category:** install_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

A PEP 517 build backend subprocess failed because a build-time dependency (e.g., Cython) is declared in pyproject.toml but not installed in the isolated build environment.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 3.x | active | — | — |

## Workarounds

1. **** (88% success)
   ```
   python -m pip install Cython numpy
python -m pip install --no-build-isolation the-package
   ```
2. **** (85% success)
   ```
   python -m pip install --only-binary=:all: --extra-index-url https://download.pytorch.org/whl/cpu the-package
   ```

## Dead Ends

- **** — The isolated build env does not inherit the outer env, so Cython is still missing inside it. (70% fail)
- **** — Without isolation, the build runs in the current env, which still lacks Cython. (65% fail)
- **** — The package source is not yours to edit; pip re-downloads the pristine sdist. (90% fail)