How to write a Dockerfile correctly

[robml]

Just playing around with pdm given how little it is mentioned anywhere else, wanted to ask if this looks about right for a Dockerfile:

# syntax=docker/dockerfile:1
FROM python:3
ENV PYTHONDONTWRITEBYTECODE=1
ENV PYTHONUNBUFFERED=1
WORKDIR /code
COPY pyproject.toml pdm.lock /code/
RUN pip install pdm && pip add --prod --no-lock --no-editable
COPY . /code/

I adopted this from the Docker website and changed it from a regular pip and requirements.txt install to the one seen on the official pdm website for a multistage Docker set up. Any ideas?

[pawamoy]

I believe you meant && pdm install instead of && pip add?

[robml]

@pawamoy btw thank you so much for your patience. I came back with fresh eyes and tried it again from scratch and it almost seemed to work. I realize that the problem comes with trying to import the django module (everything else seems to work fine).
I got this traceback from one of the containers I tried to make

Traceback (most recent call last):

  File "/code/manage.py", line 11, in main

    from django.core.management import execute_from_command_line

ModuleNotFoundError: No module named 'django'


The above exception was the direct cause of the following exception:


Traceback (most recent call last):

  File "/code/manage.py", line 22, in <module>

    main()

  File "/code/manage.py", line 13, in main

    raise ImportError(

ImportError: Couldn't import Django. Are you sure it's installed and available on your PYTHONPATH environment variable? Did you forget to activate a virtual environment?

Note I ran it without setting the PYTHONPATH because I wasn't executing any RUN commands with python in my Dockerfile. Do you think that's the cause of the issue here? And if there isn't a PDM specific way to solve the above, is there a resource you recommend I check out or is the Docker docs the best place to try and debug? Thanks again.

[robml]

@pawamoy an update on the above for future readers, it was definitely the PYTHONPATH, turns out if you are not running a Multi-Stage build you need to declare it. A weird thing I noticed is that by convention, you'd have the line:
ENV PYTHONPATH "${PYTHONPATH}:/__pypackages__/{major.minor}/lib"
However appending to the existing PYTHONPATH as above did not seem to work. What did work however almost flawlessly was instead overwriting the PYTHONPATH variable in something like this:
ENV PYTHONPATH __pypackages__/{major.minor}/lib
For those trying to just do small Docker builds I think outlining this in the docs could save beginners at least a headache @frostming .

Again thanks for the help guys.

[pawamoy]

That's what I'm trying to tell you from the beginning: whatever method you choose to run Python, PYTHONPATH must be updated somehow. It can be implicit (when you use pdm run ...) or explicit (setting it with ENV PYTHONPATH=...). Single stage or multi-stage builds are not relevant here. Sorry for not being clear enough 😅
Maybe appending didn't work because the variable is empty and you end up with PYTHONPATH=:/path/to/lib which might not be valid (starting colon).

[robml]

@pawamoy thank you :P I was just confused I think because I haven't worked with Docker much and am trying to change that. As for the empty variable, how would you solve something like that in the future btw?

[pawamoy]

Within an ENV instruction, I'm not sure 😕