What is the relationship between virtualenv and pyenv?
I recently learned how to use virtualenv and virtualenvwrapper in my workflow but I've seen pyenv mentioned in a few guides but I can't seem to get an understanding of what pyenv is and how it is different/similar to virtualenv. Is pyenv a better/newer replacement for virtualenv or a complimentary tool? If the latter what does it do differently and how do the two (and virtualenvwrapper if applicable) work together?
Answer
Pyenv and virtualenv are very different tools that work in different ways to do different things:
Pyenv is a bash extension - will not work on Windows - that intercepts your calls to python, pip, etc., to direct them to one of several of the system python tool-chains. So you always have all the libraries that you have installed in the selected python version available - as such it is good for users who have to switch between different versions of python.
VirtualEnv, is pure python so works everywhere, it makes a copy of, optionally a specific version of, python and pip local to the activate environment which may or may not include links to the current system tool-chain, if it does not you can install just a known subset of libraries into that environment. As such it is almost certainly much better for testing and deployment as you know exactly which libraries, at which versions, are used and a global change will not impact your module.
venv python > 3.3
Note that from Python 3.3 onward there is a built in implementation of VirtualEnv called venv (with, on some installations a wrapper called pyvenv - this wrapper is deprecated in Python 3.6), which should probably be used in preference. To avoid possible issues with the wrapper it is often a good idea to use it directly by using /path/to/python3 -m venv desired/env/path or you can use the excellent py python selector on windows with py -3 -m venv desired/env/path. It will create the directory specified with desired/env/path configure and populate it appropriately. In general it is very much like using VirtualEnv.
Additional Tools
There are a number of tools that it is worth mentioning, and considering, as they can help with the use of one or more of the above:
- VirtualEnvWrapper Manage and simplify the use and management of VirtualEnv - Cross Platform.
- pyenv-virtualenv, installed by pyenv-installer, which gives PyEnv tools for managing and interfacing to VirtualEnv - with this you can have a base installation that includes more than one version of python and create isolated environments within each of them - Linux/OS-X. Suggested by Johann Visagie
- PyInstaller can take your python code, possibly developed & tested under VirtualEnv, and bundle it up so that it can run one platforms that do not have your version of python installed - Note that it is not a cross compiler you will need a Windows (virtual-)machine to build Windows installs, etc., but it can be handy even where you can be sure that python will be installed but cannot be sure that the version of python and all the libraries will be compatible with your code.