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Black with Docker

web dev, kendo, yoga
・2 min read

Photo by Jan Kopřiva on Unsplash

Fromatting Python code remotely with PyCharm

I'm sure you've heard about Black, a formatter for Python. It's opinionated, but really good. One thing I disagree with - is double quotes everywhere. I prefer single. But that is disable-able.

So, what's Docker doing here? Well, you can run Black as a service. Meaning you can skip installation on a local machine and deploy straight with containers.


I've published a final image so you can just pull that from dockerhub. Or build it yourself. Here we go with a multi-stage build to make our container slim.

FROM python:3.9-alpine as builder
RUN set -eux \
        && apk add --no-cache \
                gcc \
                musl-dev \
    && pip install --upgrade pip black[d]

FROM python:alpine
COPY --from=builder /usr/local/lib/python3.9/site-packages/ /usr/local/lib/python3.9/site-packages/
COPY --from=builder /usr/local/bin/blackd /usr/local/bin/blackd
EXPOSE 45484
ENTRYPOINT ["blackd", "--bind-host", "", "--bind-port", "45484"]
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First we build a builder image, installing dependencies and Black itself. Then we just copy what we need from builder to the final image. That way we'll have around 70Mb in size.

Now you can build with:

docker build . -t blackd:latest
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Let's go to "Containers" side-menu in Portainer and smash the "Add container" button. Set:

  • name: blackd
  • image: blackd:latest OR ceeveeya/blackd:latest
  • publish port: 45484:45484

A handy screenshot:
Blackd create container

And press "Deploy".


Now when we have working Black service all is left - to use that.


Add BlackConnect plugin and set config as on the screenshot below.

BlackConnect config


Unfortunately, I couldn't find a similar extension for this IDE. But I'm not using VSCode for python development so.. ¯\_(ツ)_/¯ Let's hope somebody will make something like BlackConnect one day 😅

Now your code should be formatted every time you save it!

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