Why pyenv?

pyenv does...

• Let you change the global Python version on a per-user basis.
• Provide support for per-project Python versions.
• Allow you to override the Python version with an environment variable.
• Search commands from multiple versions of Python at a time. This may be helpful to test across Python versions with tox.

In contrast with pythonbrew and pythonz, pyenv does not...

• Depend on Python itself. pyenv was made from pure shell scripts. There is no bootstrap problem of Python.
• Need to be loaded into your shell. Instead, pyenv's shim approach works by adding a directory to your $PATH.
• Manage virtualenv. Of course, you can create virtualenv yourself, or pyenv-virtualenv to automate the process.