On: Migrating to Python 3 with pleasure

[amyjess]

I'd been a 2.7 holdout for ages, but when f-strings were greenlit for 3.6, I decided then and there that all my new personal projects would be written in 3.

I'm glad I did. F-strings are wonderful, as is pathlib and the enhanced unpacking syntax.

Since I started my current job, I've also been writing as many scripts as I can in Python 3 as well (and Docker has been a godsend for that because I can now deploy 3.6 scripts to the few servers we have that are still running RHEL 6).

[memco → amyjess]

Could you provide more info on your setup for this? I work on some EL 6 servers and would be interested in using this setup.

[Leynos → memco]

Not the OP, but replying to offer a suggestion in this respect.

I'll often do something similar to this, where I have a CLI tool that I'm not ready to deploy server-wide yet, and has hefty dependencies.

The pattern I use is to have a wrapper shell script that calls:

    docker run -it --rm --volume "$(pwd)/$1:/file_to_process:z" --user $(id -u) container-image /opt/command_to_run /fileToProcess

This runs "/opt/command_to_run /fileToProcess" inside a container as the current uid, mounting the parameter to the shell script as "/file_to_process" inside the container.

The :z mount parameter may or may not be needed depending upon whether you have SELinux enabled or not (by default, SELinux prevents countainers accessing any file on the host, and :z changes the SE context to allow access). I don't know if this is the case with EL6 tho.

The -t parameter shouldn't be used if your script is running in a pipeline (it creates a pseudo-tty). So it may be worth having some kind of conditional to remove this.

The wrapper I use also has a conditional to add the "$(pwd)" prefix to the call parameter only if the parameter is a relative path.

[amyjess → memco]

Honestly, I just wrote my Dockerfile using the example from the official Python container: https://hub.docker.com/_/python/

Then I push the image to my company's internal Docker registry, ssh into the server, and pull the image.

(also, aside from using Python 3 on RHEL 6, it also means using Python 3.6 on RHEL 7 without having to install python36u)

Edit:

Dockerfile (script name redacted)

    FROM python:3
    WORKDIR /usr/src/app

    COPY requirements.txt ./
    RUN pip install --no-cache-dir -r requirements.txt
    COPY . .

    CMD [ "python", "./redacted.py" ]

Build and push commands (company and script names redacted):

    docker build --rm -t dreg.example.com/redactedproject/redacted .
    docker push dreg.example.com/redactedproject/redacted

Pull and run on the server (same stuff redacted as above, plus I redacted the actual port number to be on the safe side):

    docker pull dreg.example.com/redactedproject/redacted
    docker run -p 1337:1337 -d --name redacted dreg.example.com/redactedproject/redacted

And at some point, I'll make proper startup scripts for them. On RHEL 7 boxes, I've made systemd unit files. On RHEL 6... well, I suppose I'll be writing initscripts soon.

[aepiepaey → memco]

If Python 3.4 is good enough, you can get it from the EPEL repos.