install pyton 3.12

#!/usr/bin/env bash
set -euo pipefail

# ============================================================
# Python 3.12.13 installer for Debian 13
#
# Everything except the final system installation stays inside
# the directory where this script is executed.
#
# System-wide installation:
#   /usr/local/bin/python3.12
#
# Debian's system Python (/usr/bin/python3) is NOT modified.
# ============================================================

PYTHON_VERSION="3.12.13"
PREFIX="/usr/local"

SCRIPT_DIR="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd)"
WORK_DIR="${SCRIPT_DIR}/python-${PYTHON_VERSION}-build"

TARBALL="Python-${PYTHON_VERSION}.tar.xz"
SOURCE_DIR="${WORK_DIR}/Python-${PYTHON_VERSION}"

URL="https://www.python.org/ftp/python/${PYTHON_VERSION}/${TARBALL}"

echo
echo "============================================================"
echo " Python ${PYTHON_VERSION} installer"
echo "============================================================"
echo
echo "Working directory:"
echo "  ${WORK_DIR}"
echo
echo "System installation:"
echo "  ${PREFIX}/bin/python3.12"
echo
echo "Debian system Python will NOT be modified."
echo

# ------------------------------------------------------------
# Check OS
# ------------------------------------------------------------

if [[ ! -f /etc/debian_version ]]; then
    echo "ERROR: This script is intended for Debian."
    exit 1
fi

# ------------------------------------------------------------
# Check sudo
# ------------------------------------------------------------

if ! command -v sudo >/dev/null 2>&1; then
    echo "ERROR: sudo is required."
    exit 1
fi

# ------------------------------------------------------------
# Check architecture
# ------------------------------------------------------------

ARCH="$(uname -m)"

if [[ "$ARCH" != "x86_64" ]]; then
    echo "ERROR: This script expects x86_64."
    echo "Detected: ${ARCH}"
    exit 1
fi

# ------------------------------------------------------------
# Check if exact version is already installed
# ------------------------------------------------------------

if [[ -x "${PREFIX}/bin/python3.12" ]]; then
    INSTALLED_VERSION="$("${PREFIX}/bin/python3.12" --version 2>&1 || true)"

    if [[ "$INSTALLED_VERSION" == "Python ${PYTHON_VERSION}" ]]; then
        echo "Python ${PYTHON_VERSION} is already installed:"
        echo "  ${PREFIX}/bin/python3.12"
        exit 0
    fi
fi

# ------------------------------------------------------------
# Create local working directory
# ------------------------------------------------------------

mkdir -p "$WORK_DIR"

# ------------------------------------------------------------
# Install build dependencies
#
# These are system-wide package changes and require sudo.
# ------------------------------------------------------------

echo "[1/7] Installing build dependencies..."

sudo apt-get update

sudo apt-get install -y \
    build-essential \
    wget \
    ca-certificates \
    libssl-dev \
    zlib1g-dev \
    libbz2-dev \
    libreadline-dev \
    libsqlite3-dev \
    libncursesw5-dev \
    xz-utils \
    tk-dev \
    libxml2-dev \
    libxmlsec1-dev \
    libffi-dev \
    liblzma-dev

# ------------------------------------------------------------
# Download Python source
# ------------------------------------------------------------

echo
echo "[2/7] Downloading Python ${PYTHON_VERSION}..."

cd "$WORK_DIR"

if [[ ! -f "$TARBALL" ]]; then
    wget --https-only -O "$TARBALL" "$URL"
else
    echo "Source archive already exists:"
    echo "  ${WORK_DIR}/${TARBALL}"
fi

# ------------------------------------------------------------
# Extract source
# ------------------------------------------------------------

echo
echo "[3/7] Extracting source..."

if [[ ! -d "$SOURCE_DIR" ]]; then
    tar -xf "$TARBALL"
fi

cd "$SOURCE_DIR"

# ------------------------------------------------------------
# Configure
# ------------------------------------------------------------

echo
echo "[4/7] Configuring Python ${PYTHON_VERSION}..."

./configure \
    --prefix="$PREFIX" \
    --with-ensurepip=install

# ------------------------------------------------------------
# Compile
# ------------------------------------------------------------

echo
echo "[5/7] Compiling Python..."

make -j"$(nproc)"

# ------------------------------------------------------------
# Install system-wide
#
# altinstall deliberately avoids replacing python3.
# ------------------------------------------------------------

echo
echo "[6/7] Installing Python system-wide..."

sudo make altinstall

# ------------------------------------------------------------
# Verify
# ------------------------------------------------------------

echo
echo "[7/7] Verifying installation..."

PYTHON_BIN="${PREFIX}/bin/python3.12"

if [[ ! -x "$PYTHON_BIN" ]]; then
    echo
    echo "ERROR: Installation completed but ${PYTHON_BIN} was not found."
    exit 1
fi

INSTALLED_VERSION="$("$PYTHON_BIN" --version 2>&1)"

if [[ "$INSTALLED_VERSION" != "Python ${PYTHON_VERSION}" ]]; then
    echo
    echo "ERROR: Wrong Python version installed."
    echo "Expected: Python ${PYTHON_VERSION}"
    echo "Found:    ${INSTALLED_VERSION}"
    exit 1
fi

echo
echo "============================================================"
echo " SUCCESS"
echo "============================================================"
echo
echo "Python:"
echo "  ${INSTALLED_VERSION}"
echo
echo "Executable:"
echo "  ${PYTHON_BIN}"
echo
echo "System-wide command:"
echo "  python3.12"
echo
echo "Debian system Python:"
python3 --version
echo
echo "Build files remain in:"
echo "  ${WORK_DIR}"
echo
echo "============================================================"