Virtual Environments

A virtual environment is an isolated Python environments. It has it's own installed site-packages which can be different from the systems site-packages.

TL;DR: pipenv is your friend; it allows you to forget about the others.

virtualenv

virtualenv was created by Ian Bicking. The first version on PyPI is from 2007.

pyvenv

Was deprecated in favour of python -m venv. It was removed with Python 3.8.

venv

The venv module was added in Python 3.3 with PEP 405 (2012).

pyenv

pyenv lets you switch between multiple versions of Python.

Installation: See GitHub

Usage:

$ pyenv install --list
Available versions:
  2.1.3
  [...]
  3.8.1
  3.9-dev
  activepython-2.7.14
  activepython-3.5.4
  activepython-3.6.0
  anaconda-1.4.0
  [... a lot more; including anaconda, miniconda, activepython, ironpython, pypy, stackless, ....]

$ pyenv install 3.8.1
Downloading Python-3.8.1.tar.xz...
-> https://www.python.org/ftp/python/3.8.1/Python-3.8.1.tar.xz
Installing Python-3.8.1...
Installed Python-3.8.1 to /home/moose/.pyenv/versions/3.8.1

$ pyenv versions
* system (set by /home/moose/.pyenv/version)
  2.7.16
  3.5.7
  3.6.9
  3.7.4
  3.8-dev

$ python --version
Python 2.7.17
$ pip --version
pip 19.3.1 from /home/moose/.local/lib/python3.6/site-packages/pip (python 3.6)

$ mkdir pyenv-experiment && echo "3.8.1" > "pyenv-experiment/.python-version"
$ cd pyenv-experiment

$ python --version
Python 3.8.1
$ pip --version
pip 19.2.3 from /home/moose/.pyenv/versions/3.8.1/lib/python3.8/site-packages/pip (python 3.8)

pipenv

pipenv automatically creates and manages a virtualenv for your projects, as well as adds/removes packages from your Pipfile as you install/uninstall packages. It also generates the Pipfile.lock, which is used to produce deterministic builds. It helps creating reproducible environments.

pipenv uses virtualenv and pyenv.

Usage

First, create a virtual environment:

$ pipenv --python 3.8
Creating a virtualenv for this project…
Pipfile: /home/moose/GitHub/clana/Pipfile
Using /home/moose/.pyenv/versions/3.8.1/bin/python3.8 (3.8.1) to create virtualenv…
⠏ Creating virtual environment...Already using interpreter /home/moose/.pyenv/versions/3.8.1/bin/python3.8
Using base prefix '/home/moose/.pyenv/versions/3.8.1'
New python executable in /home/moose/.local/share/virtualenvs/clana-oPEDiD9W/bin/python3.8
Also creating executable in /home/moose/.local/share/virtualenvs/clana-oPEDiD9W/bin/python
Installing setuptools, pip, wheel...
done.
Running virtualenv with interpreter /home/moose/.pyenv/versions/3.8.1/bin/python3.8

✔ Successfully created virtual environment! 
Virtualenv location: /home/moose/.local/share/virtualenvs/clana-oPEDiD9W
requirements.txt found, instead of Pipfile! Converting…
✔ Success! 
Warning: Your Pipfile now contains pinned versions, if your requirements.txt did. 
We recommend updating your Pipfile to specify the "*" version, instead.

Activate the environment:

$ pipenv shell
Launching subshell in virtual environment…
 . /home/moose/.local/share/virtualenvs/clana-oPEDiD9W/bin/activate

$ pip --version
pip 20.0.2 from /home/moose/.local/share/virtualenvs/clana-oPEDiD9W/lib/python3.8/site-packages/pip (python 3.8)

Set your Pipfile.lock:

$ pipenv lock
Locking [dev-packages] dependencies…
Locking [packages] dependencies…
✔ Success! 
Updated Pipfile.lock (310e7d)!

Make sure your environment has exactly the stuff installed that you need:

$ pipenv sync
Installing dependencies from Pipfile.lock (310e7d)…
  🐍   ▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉▉ 14/14 — 00:00:06
All dependencies are now up-to-date!

Docker

If you want more isolation, have a look at Docker. I use the python:3.8-slim-buster (February 2020).

The Dockerfile can then look like this:

FROM python:3.8-slim-buster

# Update and install extra packages
RUN apt-get update && apt-get install -y git build-essential

# Install project dependencies
COPY requirements.txt /opt/app/requirements.txt
WORKDIR /opt/app
RUN pip install -r requirements.txt

# Install project
COPY . /opt/app
RUN pip install . --no-deps

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