# error: command 'gcc' failed with exit status 1
    building 'foo._speedups' extension

- **ID:** `python/setuptools-cython-build-ext-failed`
- **Domain:** python
- **Category:** install_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

A package with C extensions (Cython) is being built from sdist but the compiler toolchain or Python development headers are missing/incompatible, so gcc fails during the extension build.

## Version Compatibility

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

## Workarounds

1. **** (90% success)
   ```
   Install a prebuilt wheel: pip install --only-binary=:all: foo  # avoids compilation entirely
   ```
2. **** (82% success)
   ```
   Install the toolchain: sudo apt install build-essential python3-dev  # then pip install foo
   ```

## Dead Ends

- **** — Disabling isolation doesn't install gcc or python-dev headers; the compiler is still absent. (65% fail)
- **** — Build tooling versions don't affect the missing system compiler/headers; compilation still fails. (60% fail)