Setting Up Python: pyenv, pyenv-virtualenv, poetry

These are steps to install and set up Python on a Mac.

Skip to the sections below:

Additional reference on alternative choices: Real Python: An Effective Python Environment

pyenv: Python Version Manager

Docs: GitHub - pyenv/pyenv

A Python Version Manager allows usage of different version of python, and manages which Python to use in the current session, globally, or on a per-project basis.

[Prep: Mac OS X]: Install Xcode Command Line Tools

$ sudo rm -rf /Library/Developer/CommandLineTools

$ xcode-select --install

When running Mojave or higher (10.14+) you will also need to install the additional SDK headers:

$ sudo installer -pkg /Library/Developer/CommandLineTools/Packages/macOS_SDK_headers_for_macOS_10.14.pkg -target /

Install pyenv

$ brew update
$ brew install openssl readline sqlite3 xz zlib
$ brew install pyenv

Update .bash_profile or .zshrc

Add pyenv init to your shell to enable shims and autocompletion.

Make sure eval “$(pyenv init -)” is placed toward the end of the shell configuration file since it manipulates PATH during the initialization.

$ echo -e ‘if command -v pyenv 1>/dev/null 2>&1; then\n  eval$(pyenv init -)\nfi’ >> ~/.zshenv

Restart your shell so the path changes take effect and begin using pyenv.

$ exec "$SHELL"

pyenv Workflow Commands

Dosc: Command Reference

Make 3.7.4 globally available so there is no messing with our system python:

$ pyenv versions

$ pyenv install --list
$ pyenv install 3.7.4

$ pyenv global 3.7.4

pyenv-virtualenv: Virtual Environment

Docs: GitHub - pyenv/pyenv-virtualenv

A Python Virtual Environment Manager allows setting different projects with its own set of version dependencies. When a package is installed in a virtual environment, it is kept in isolation from other Python environments you may have.

Install pyenv-virtualenv

$ brew install pyenv-virtualenv

Update .bash_profile or .zshrc

$ echo 'eval "$(pyenv virtualenv-init -)"' >> ~/.zshenv

pyenv-virtualenv Workflow Commands

Docs: Command Reference

Set up a new virtual environment and activate it

# Create virtual environment
$ pyenv virtualenv 3.7.4 my-env

# Activate virtual environment
$ pyenv activate my-env

# Exit virtual environment
(my-env)$ pyenv deactivate

Set up new virtual environments within a directory

pyenv-virtualenv allows configuring a virtual environment using the pyenv local command and have pyenv-virtualenv auto-activate the right environments as you switch to different directories

When entering into the directory, pyenv will also activate the new-project virtual environment, and will deactivate the virtual environment on exiting the directory.

# Set up two new virtual environments, env1 and env2
$ pyenv virtualenv 3.7.4 env1
$ pyenv virtualenv 3.7.4 env2

# Set up the env1 virtual environment in a new directory
$ mkdir proj1
$ cd proj1
$ pyenv local env1(env1)$ # env1 virtual environment is now active in this directory

# Set up the env2 virtual environment in a new directory
(env1)$ mkdir ../proj2
(env1)$ cd ../proj2
$ pyenv local env2
# Check that the proj2 directory has the env2 virtual environment activated
(env2)$ pyenv versions
  system
  3.7.4
  3.7.4/envs/env2
  3.7.4/envs/env2
  env1
* env2 (set by /Users/duncanleung/proj2/.python-version)

Check the Installation

The correct installation should reference the $PATH from .../.pyenv/shims/python.

$ which Python
  /Users/MACHINE_NAME/.pyenv/shims/python

If the $PATH is referencing /usr/bin/python then pyenv-virtualenv needs to be added to the shell in ~/.zshenv or ~/.bash_profile.

$ which Python
  /usr/bin/python # This is wrong!

Check the version of python to see if the correct version is being used.

$ python --version
  Python 3.7.4

Delete an existing virtualenv

$ pyenv virtualenvs
$ pyenv uninstall env1

Poetry: Package Manager

Docs: GitHub - poetry

Package managers work in tandem with virtual environments, isolating the packages you install in one Python environment from another.

Package manager generally create a lock file to act as a snapshot of the precise set of packages installed, including direct dependencies as well as their sub-dependencies.

poetry also creates a pyproject.toml file which contains metadata about the project as well as dependency versions.

poetry has a benefit over pipenv because it keeps track of which packages are subdependencies, allowing cleaner uninstalls to also remove dependencies of a package

Install

Install poetry

$ curl -sSL https://raw.githubusercontent.com/sdispater/poetry/master/get-poetry.py | python

$ source $HOME/.poetry/env

Install tab completions for poetry

# Bash (macOS/Homebrew)
poetry completions bash > $(brew --prefix)/etc/bash_completion.d/poetry.bash-completion

Update poetry

poetry self:update

poetry Workflow Commands

Docs: Command Reference

Install packages with poetry add.

Install dev dependency packages with poetry add --dev

# Install the requests package and its dependencies
$ poetry add requests

# Uninstall the requests package and its dependencies
$ poetry remove requests