chpython

Changes the current Python.

What is it?

It's a way to seamlessly switch between multiple Python installations. It's mostly designed for setting a "default" Python interpreter for running scripts or providing an interactive shell, rather than setting a Python interpreter for a specific project (virtualenv and friends is a better tool for per-project Python installations).

What is it not?

chpython is not a tool to:

Replace virtualenv. chpython is not designed to switch between Pythons on a per-project basis.
Install Python. I do not plan to add support for downloading and compiling Python to chpython. It is expressly for managing installations.

What does it do?

chpython lets you switch easily between different versions of Python that you have installed in ~/.pythons. It switches between them by:

Updating $PATH.
Aliasing *3 bins to their basename (e.g., python3 can be called using python) (not implemented yet).
Calling hash -r to update the command-lookup hashtable.

You can return to the default (system) Python by calling:

$ chpython system

Calling chpython system will completely restore the environment you had before calling chpython VERSION.

You can also execute a command using any installed version of Python, without updating $PATH or any other environment variables, by calling:

$ chpython exec VERSION args...

For example, you can call python -V on an ancient version of Python you have installed for some reason:

$ chpython exec 2.5 python -V

chpython supports fuzzy matching of Python versions, so chpython 2.7 will execute the latest version of Python 2.7 it can find. You can also specify a full version: chpython 2.7.10.

What does it not do?

chpython does not:

Hook into cd.
Install executable shims (like pyenv).
Does not muck with your prompt or anything but the $PATH variable.

What does it require?

bash (it may work with zsh, but I haven't tested it)

How do I install it?

Clone the repository (git clone https://github.com/mdippery/chpython.git).
Copy or symlink share/chpython/chpython.sh to /usr/local/share/chpython, or anywhere else you feel like putting it. Or keep it where it is after cloning the repo, I don't care.
Add source /where/you/put/share/chpython/chpython.sh somewhere in ~/.bashrc.
Optionally, set a Python version by adding chpython VERSION to your ~/.bashrc file. If you don't do this, your system's Python will be used by default, but you can use a different Python on a per-shell basis by calling chpython VERSION manually.

Why not use...

...virtualenv?

Virtualenv is a great solution for setting up a specific Python version to use on a per-project basis, but I have never liked using it to set a default python to use for "everyday" scripts in my shell, since it involves setting up a "global" virtualenv anyway. I also don't like how the default virtualenv activate scripts mucks with things in my environment, such as $PS1 (and virtualenv's default $PS1 is ugly). Generally speaking, pointing your shell to a "new" Python is as simple as adding its bin directory to your $PATH; nothing else is needed if you installed it normally.

I compile versions of Python to use by default in my shell to ~/.pythons. I wanted a quick way to switch between different versions, and was inspired by chruby to write a bash script to handle that switching seamlessly for me.

...Conda (Anaconda, Miniconda)?

Conda and its various incarnations could be used for a similar purpose, but personally I find them to be far too heavyweight for the relatively simple tasking of providing and managing default Python installations.

mdippery / chpython