Setting up a Mac development environment with pyenv and pyenv-virtualenv

In this guide, you'll set up a local Python development environment with multiple Python versions, managed by pyenv.

This guide differs from the Google Cloud Python development instructions because developers of samples and libraries need to be able to use multiple versions of Python to test their code.

Before you begin

[Optional] Install homebrew.

Installing pyenv and pyenv-virtualenv

Install pyenv.

I (tswast@) use homebrew to install it.
```
brew update
brew install pyenv
```
Install the pyenv-virtualenv plugin.
```
brew install pyenv-virtualenv
```
Append the following to your ~/.bashrc:
```
eval "$(pyenv init -)"
eval "$(pyenv virtualenv-init -)"
```
Note that this also works with ZSH.
Reload your shell.
```
source ~/.bashrc
```
Verify that you are now using the pyenv Python shim.
```
$ which python
/Users/tswast/.pyenv/shims/python
```

Installing multiple Python versions

See the available Python versions with
```
pyenv install --list
```
The Python versions are at the top of the long list. If the Python version you want isn't listed, you may need to upgrade your pyenv with homebrew.
```
brew update
brew upgrade pyenv
```
Compile the necessary Python versions with pyenv. Use the latest release of the versions you wish to test against.

As of August 8, 2018 my (tswast@) Python versions are:
- 2.7.15 (latest 2.7.x release)
- 3.5.4 (latest 3.5.x release)
- 3.6.4 (latest 3.6.x release)
- 3.7.0 (latest 3.7.x release)

Using pyenv and pyenv-virtualenv to manage your Python versions

Set the local Python version(s) with pyenv local

# pyenv local [name of virtualenv] [list of python versions to use]
pyenv local python-docs-samples 3.6.4 3.7.0 3.5.4 2.7.15