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From what I understand about Docker, it's a tool used for virtual environments. In their lingo, its called "containerization". This is more or less what Python's virtualenv does. However, you can use virtualenv in Docker. So, is it a virtual environment inside a virtual environment? I'm confused as to how this would even work, so could someone please clarify?

nbro
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danielschnoll
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    This is a good question, but will likely get closed as off-topic. virtualenv is not a real isolation, it's a poor man's isolation using path hacks and symlinks - you're still within your own operating system. Docker provides more isolation, but not as much as a full-on virtual machine. You could think of a container as a middle-ground between a virtualbox (heavy, expensive) and a virtualenv (light, cheap). Creating a virtualenv inside a container does not make much sense because the isolation is already provided by docker, there would be not much point in doing that. – wim Jun 21 '18 at 18:06
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    Possible duplicate of [what is the difference between vagrant, docker, virtualenv or just a virtual machine?](https://stackoverflow.com/questions/40177240/what-is-the-difference-between-vagrant-docker-virtualenv-or-just-a-virtual-mac) – phd Jun 21 '18 at 19:20

4 Answers4

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A virtualenv only encapsulates Python dependencies. A Docker container encapsulates an entire OS.

With a Python virtualenv, you can easily switch between Python versions and dependencies, but you're stuck with your host OS.

With a Docker image, you can swap out the entire OS - install and run Python on Ubuntu, Debian, Alpine, even Windows Server Core.

There are Docker images out there with every combination of OS and Python versions you can think of, ready to pull down and use on any system with Docker installed.

sp0gg
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    Additionally there are [distroless images](https://github.com/GoogleContainerTools/distroless) for 'several popular programming languages' (including Python) from Google that 'contain only the programming language runtime' - from [ArchWiki/Docker](https://wiki.archlinux.org/index.php/Docker#Distroless) – muthuh Nov 22 '20 at 11:22
  • For virtual environments that encapsulate more than just Python dependencies (like Python itself), check out nixpkgs/nix-shell (also works on macOS). Docker on macOS for development/hot reloading of code using volumes is slow because on macOS, Docker runs inside a VM - and files/file system events need to be translated from the macOS file system to ext4 or similar. – Tobias Bergkvist Mar 01 '22 at 15:21
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Python virtual environment will "containerize" only Python runtime i.e. python interpreter and python libraries whereas Docker isolates the whole system (the whole file-system, all user-space libraries, network interfaces) . Therefore Docker is much closer to a Virtual Machine than virtual environment.

jil
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    Is there any benefit in creating a virtual environment inside a docker container considering that the container will only serve a flask web app. – thanos.a Apr 23 '20 at 22:04
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Adding to the above: there is a case for combining docker and venv: some OSs ship with python installed to provide 'OS-near' apps, e.g., to my knowledge, apt on debian (and its derivatives). The python venv enables a developer to ship a python app which requires a different interpreter version without affecting the shipped-with-the-OS python. Now, since Docker 'isolates the whole OS' as stated above, the same applies to a Docker image. Hence, in my view, if a Docker image is required/desired, it is best practice to create a venv inside the Docker image for your python app.

Blindfreddy
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    Would this slow down response time (two levels of virtualization)? – Andrew Swift Feb 02 '19 at 13:08
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    Python virtual environment changes the python environment it does not virtualize the execution of the python interpreter. Docker container is not virtualized unless it is executed with a hypervisor (Docker Machine). – Morten Mar 20 '19 at 09:43
  • I still think that it will be tedious for me to mount docker inside an operating system, I usually do this, I program in a shell language all dependencies of the project external to pytohn and I execute them automatically, let's say in production via ssh – Alex Ancco Cahuana Sep 03 '20 at 15:30
  • _which requires a different interpreter version_ - This is false. The venv is the same version as the OS interpreter that created it – OneCricketeer Dec 06 '21 at 14:36
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"a virtual environment, a self-contained directory tree that contains a Python installation for a particular version of Python, plus a number of additional packages"

A docker container provides a higher level of abstraction/isolation, it can has its own "process space, file system, network space, ipc space, etc."

Michael.Sun
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