Python 2 reached its end of life on January 1, 2020, meaning it no longer receives security updates or official support. Despite this definitive sunset date, there are still legitimate scenarios where maintaining or initializing a legacy environment requires installing Python 2. This might involve supporting a decades-old codebase within a specific industrial control system, running a proprietary scientific computation tool that has not been migrated, or simply preserving historical infrastructure for archival research. Understanding how to install Python 2 safely and correctly is crucial for these situations, allowing you to isolate the interpreter without interfering with modern Python 3 workflows on your machine.
Understanding the Risks and Isolation Strategies
Before you install Python 2, it is essential to acknowledge that running end-of-life software introduces significant security vulnerabilities. You should never use Python 2 for any task involving network exposure, handling sensitive data, or processing untrusted input. The primary strategy for managing this risk is strict environmental isolation. Instead of making Python 2 your system's default interpreter, you should contain it entirely within a virtual environment, a container, or a dedicated virtual machine. This containment ensures that the old interpreter and its libraries are walled off from your primary development system, mitigating potential attack surfaces.
Installing Python 2 on macOS and Linux
On Unix-like systems, the recommended approach to install Python 2 is not to use the system package manager for the default distribution, but to leverage a version manager. Tools like `pyenv` are ideal because they compile the interpreter in your user space and allow you to switch between multiple Python versions seamlessly. To install Python 2.7 using `pyenv`, you first add the specific version string (`2.7.18`) to your local or global configuration. The process involves downloading the source code, compiling it, and linking the binary, which keeps the installation clean and modular without altering system directories.
Using Package Managers with Caution
If you cannot use a version manager, most Linux distributions and macOS still provide Python 2.7 in their legacy package repositories. On Debian or Ubuntu, you would update the package list and install `python2.7` directly. However, this method requires caution, as placing binaries in system paths like `/usr/bin` can conflict with scripts that rely on Python 3. You should verify the installation path carefully and avoid setting Python 2 as the default `python` symlink. On Red Hat-based systems, the package is typically named `python2`, and the process follows similar principles of adding legacy software to the system path.
Setting Up a Contained Environment
Once the interpreter binary is on your system, the critical step is to create an isolated environment using `virtualenv`. You must use a version of `virtualenv` that is compatible with Python 2, which often means installing an older version of the tool itself (e.g., `virtualenv==16.7.9`). You then invoke this specific virtualenv binary, pointing it to your Python 2 interpreter executable. This command generates a folder containing a copy of the interpreter and a clean `site-packages` directory. Activating this environment ensures that any `pip` or `python` commands you run apply only to the legacy project, keeping the global system clean and stable.
