multiple Python versions on Ubuntu

You can install and manage multiple Python versions on Ubuntu using the pyenv tool or by using the Deadsnakes PPA (Personal Package Archive) with apt. The pyenv method is generally recommended as it is safer and user-level, while the PPA method is good for system-wide access.

Method 1: Using pyenv (Recommended for development)

pyenv allows you to manage multiple Python versions and switch between them easily without affecting the system's default Python installation.

Install system dependencies: These packages are necessary to build Python from source, which pyenv does.

bash

sudo apt update
sudo apt install git curl make build-essential libssl-dev zlib1g-dev libbz2-dev libreadline-dev libsqlite3-dev wget llvm libncurses5-dev libncursesw5-dev xz-utils tk-dev libffi-dev liblzma-dev python3-openssl

Install pyenv: Run the automatic installer script provided by pyenv.

bash
```
curl https://pyenv.run | bash
```

Configure your shell environment: Add the following lines to your ~/.bashrc (or ~/.zshrc if you use Zsh) file to ensure pyenv loads correctly.

bash

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

Reload your shell: Close and reopen your terminal, or run the following command to apply the changes to your current session:

bash
```
source ~/.bashrc
```
Install desired Python versions: Now you can install specific Python versions using pyenv. For example, to install Python 3.8.0 and 3.12.0:

bash
```
pyenv install 3.8.0
pyenv install 3.12.0
```
Switch between versions:
- To set a global default for your user: pyenv global 3.12.0.
- To set a local version for a specific project directory: pyenv local 3.8.0.

Method 2: Using the Deadsnakes PPA (System-wide installation)

The Deadsnakes PPA offers various Python versions packaged for Ubuntu, allowing installation via apt without manually compiling from source. This method installs Python versions system-wide.

Add the Deadsnakes PPA:

bash

sudo add-apt-repository ppa:deadsnakes/ppa
sudo apt update

Install specific Python versions: Install the desired versions (e.g., Python 3.8 and 3.12).

bash
```
sudo apt install python3.8
sudo apt install python3.12
```
Verify installations: The executables will be available as python3.8 and python3.12.

bash
```
python3.8 --version
python3.12 --version
```

Install pip for each version: pip must be installed separately for each version.

bash

sudo apt install python3.8-distutils # Install distutils first if needed
curl -sS https://bootstrap.pypa.io/get-pip.py | python3.8

sudo apt install python3.12-distutils # Install distutils first if needed
curl -sS https://bootstrap.pypa.io/get-pip.py | python3.12

Important Note: Avoid modifying the default system Python symlink (/usr/bin/python3) directly, as system tools rely on it and changing it can cause your operating system to break. The methods above allow different versions to coexist safely. For project-specific dependencies, always use Python virtual environments