# ERROR: Could not build wheels for mypkg, which is required to install pyproject.toml-based projects

× Building wheel for mypkg (pyproject.toml) did not run successfully.
│ exit code: 1
╰─> ModuleNotFoundError: No module named 'setuptools'

- **ID:** `python/setuptools-missing-build-system-requires`
- **Domain:** python
- **Category:** install_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

The project's pyproject.toml declares a [build-system] table whose 'requires' omits setuptools (or declares an empty list), so the isolated build env lacks the backend.

## Version Compatibility

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

## Workarounds

1. **** (97% success)
   ```
   [build-system]
requires = ["setuptools>=68", "wheel"]
build-backend = "setuptools.build_meta"
   ```
2. **** (90% success)
   ```
   python -m pip install 'setuptools>=68' wheel
python -m pip install --no-build-isolation mypkg
   ```

## Dead Ends

- **** — Build isolation creates a fresh env; the current venv's setuptools is not visible. (85% fail)
- **** — Then the build uses the current Python's setuptools, which may be absent or too old. (75% fail)