NOTE: You can activate multiple versions at the same time, including multiple versions of Python2 or Python3 simultaneously. This allows for parallel usage of Python2 and Python3, and is required with tools like tox. For example, to instruct Pyenv to first use your system Python and Python3 (which are e.g. 2.7.9 and 3.4.2) but also have Python 3.3.6, 3.2.1, and 2.5.2 available, you first pyenv install the missing versions, then set pyenv global system 3.3.6 3.2.1 2.5.2. Then you'll be able to invoke any of those versions with an appropriate pythonX or pythonX.Y name. You can also specify multiple versions in a .python-version file by hand, separated by newlines. Lines starting with a # are ignored.
pyenv 正解
https://github.com/pyenv/pyenv