Install Python 3 on raspberry pi and make it the system default

As of this blog post, the raspberry pi still ships with python2.7 as the default. There's also not really an easy way to install python3.8 (again the latest as of this post) as the system default.

I used a global pyenv so that the global version can be upgraded and changed easily.

The below script will automatically download, compile, and set python3.8.5 as the new system default for your raspberry pi. No prompts necessary.

You can run the gist to automatically do this:

curl 'https://gist.githubusercontent.com/stephen-mw/341c8194aefb694939b366204156037c/raw/fe2fc6060792dbe3e98bc3fc7830229e0d657bdf/install_python38_on_py.sh' | sudo bash

Or just copy below into your script and execute it:

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

# This script downloads, compiles, and installs python3.8 as the system default

export VERSION=3.8.5

apt install -y       \
    build-essential  \
    libbz2-dev       \
    libffi-dev       \
    liblzma-dev      \
    libncurses5-dev  \
    libncursesw5-dev \
    libreadline-dev  \
    libsqlite3-dev   \
    libssl-dev       \
    llvm             \
    python-openssl   \
    python-pip       \
    tk-dev           \
    xz-utils         \
    zlib1g-dev

export OLD_PIP=$(which pip)
export NEW_PIP=${OLD_PIP}2.7

mv ${OLD_PIP} ${NEW_PIP}
ln -s ${NEW_PIP} ${OLD_PIP}

export PYENV_ROOT=/etc/pyenv
export PATH="$PYENV_ROOT/bin:$PATH"

if [[ -d "${PYENV_ROOT}" ]]; then
    rm -rfv -- "${PYENV_ROOT}"
fi

git clone https://github.com/pyenv/pyenv.git ${PYENV_ROOT}

# Can't fit in /tmp because it's a ramfs
local TMPDIR=${PYENV_ROOT}/tmp
mkdir ${TMPDIR}

# The latest version as of now
echo "Setting system python to ${VERSION}. This may take several minutes..."
CFLAGS="-O2" TMPDIR=${TMPDIR} pyenv install ${VERSION}

rm -rf -- "${TMPDIR}"

# Set the global version
pyenv global ${VERSION}

# Latest
update-alternatives --install $(which python) python /etc/pyenv/versions/${VERSION}/bin/python 1
update-alternatives --install $(which pip) pip /etc/pyenv/versions/${VERSION}/bin/pip 1

# 2.7
update-alternatives --install $(which python) python /usr/bin/python2.7 2
update-alternatives --install $(which pip) pip /usr/bin/pip2.7 2

# Lastly, set the system python to our new version
update-alternatives --set python /etc/pyenv/versions/${VERSION}/bin/python
update-alternatives --set pip /etc/pyenv/versions/${VERSION}/bin/pip

pip install -U pip

cat <<"HELP"

Python${VERSION} is now your system default.

If you want to roll your system back to 2.7, simply run:

    sudo update-alternatives --set python /usr/bin/python2.7
    sudo update-alternatives --set pip /usr/bin/pip2.7

HELP