wcDogg/python-install-multiple-versions-on-linux.md

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    Install Multiple Versions of Python on Linux

Tools like Nox run tests against multiple versions of Python. Here's how to use pyenv to manage multiple versions of Python and make those versions available during testing.
Existing Python?

I've used distros where no Python is installed and where multiple versions are installed. If it's reasonable, go for a blank slate by uninstalling existing Python.
# See what's there
dpkg -l

# Purge
sudo apt purge python3 
sudo apt purge python3.10 

# Clean up after purge
sudo apt autoremove
sudo apt clean
Install pyenv

# Install pyenv from ~/
curl https://pyenv.run | bash

# Set up Bash
# https://github.com/pyenv/pyenv#set-up-your-shell-environment-for-pyenv
echo 'export PYENV_ROOT="$HOME/.pyenv"' >> ~/.bashrc
echo 'command -v pyenv >/dev/null || export PATH="$PYENV_ROOT/bin:$PATH"' >> ~/.bashrc
echo 'eval "$(pyenv init -)"' >> ~/.bashrc
echo 'eval "$(pyenv virtualenv-init -)"' >> ~/.bashrc

# Restart shell
exec "$SHELL"

# Install build dependencies
# https://github.com/pyenv/pyenv/wiki#suggested-build-environment
sudo apt update
sudo apt -y install make build-essential libssl-dev zlib1g-dev libbz2-dev libreadline-dev libsqlite3-dev wget curl llvm libncursesw5-dev xz-utils tk-dev libxml2-dev libxmlsec1-dev libffi-dev liblzma-dev
Install Python

# List versions that can be installed
pyenv install -l

# Install needed versions
pyenv install 3.7.9 3.8.10 3.9.13 3.10.6

# Confirm installed
pyenv versions

# Set the global version
pyenv global 3.10.6

# See which version is currently in use
pyenv version
python --version

# Confirm pip - should point to pyenv
pip --version

# Update the global version
python -m pip install --upgrade pip setuptools wheel

# Refresh the Python environment
pyenv rehash

# Uninstall versions
pyenv uninstall 3.10.4
Install pipx

Use pipx to install end-user apps that should be available across projects - Nox, Scrapy, Poetry.
# Install
pip install --user pipx

# Note path warnings
WARNING: The script userpath is installed in '/home/wcd/.local/bin' which is not on PATH.
WARNING: The script pipx is installed in '/home/wcd/.local/bin' which is not on PATH.

# Add the needed path to .bashrc
echo 'export PATH=$PATH:"/home/wcd/.local/bin"' >> ~/.bashrc
exec "$SHELL"

# Restart shell and test
pipx

# Update
python -m pip install --user -U pipx

# Install a package
# https://pypa.github.io/pipx/examples/
pipx install pycowsay
Make Multiple Versions Available

When it’s time to run Nox tests, make all the needed versions available by running this in the project directory:
pyenv local 3.7.9 3.8.10 3.9.13 3.10.6
venv

Tools like Poetry + Scrapy create their own virtual environments. For other projects, you need to create a virtual environment. Here's how.
# Create a project directory and cd into it
mkdir test-project
cd test-project

# Create virtual environment
python -m venv venv

# Activate environment
source venv/bin/activate
# Prompt now displays [venv]

# Install the minimums
python -m pip install --upgrade pip setuptools wheel

# Open folder in VS Code
code .

# Deactivate venv in bash
deactivate