build

# Building and Testing CPython

## Building CPython

**ONLY build in a `build/` subdirectory** at repo root. Never build in the source tree.

### Setup and Configuration

```bash
# Build directory setup
REPO_ROOT=<path-to-cpython-git-repo>
BUILD_DIR=$REPO_ROOT/build
```

#### ccache Setup (Recommended)

ccache dramatically speeds up rebuilds by caching compilation results. Check if available:

```bash
which ccache
```

**If ccache is not installed**:
- macOS (Homebrew): Install directly with `brew install ccache` (no sudo required)
- Containerized/root environments: Install directly with `apt-get install -y ccache` or `dnf install -y ccache`
- Otherwise, ask the user for permission to install:
  - Debian/Ubuntu: `sudo apt-get install ccache`
  - Fedora/RHEL: `sudo dnf install ccache`

**Configure with ccache** (if available):
```bash
cd $BUILD_DIR && CC="ccache gcc" ../configure --with-pydebug
```

**Configure without ccache** (fallback):
```bash
cd $BUILD_DIR && ../configure --with-pydebug
```

#### Performance/Benchmarking Builds

When doing benchmarking or performance measurement of C code changes, **omit `--with-pydebug`** from configure:

```bash
cd $BUILD_DIR && CC="ccache gcc" ../configure  # No --with-pydebug
```

Debug builds have significant overhead that distorts performance measurements. However, **do not use `--enable-optimizations`** unless explicitly asked—it enables PGO (Profile-Guided Optimization) which is slow to compile. Non-PGO release builds are sufficient for the majority of performance comparison work.

```bash
# Build using all CPU cores (initial or incremental)
make -C $BUILD_DIR -j $(nproc)
```

**Platform notes**:
- Linux: `BUILT_PY=$BUILD_DIR/python`
- macOS: `BUILT_PY=$BUILD_DIR/python.exe` (note .exe extension)
- Windows: Ask user how to build (uses Visual Studio, different process)

### Argument Clinic

After editing `.c` files that change function signatures, docstrings, or argument specs:
```bash
make -C $BUILD_DIR clinic
```

**NEV