Docker creation with web service in complex architecture

I need to create a docker containing some code and a small flask server to expose some part of the code. But I struggle to make it working to my complex file architures.
My files are organized as :

main_project
    --sub_part_1
        --repo_1
            --some_code.py
        --repo_2
            --app.py
            --Dockerfile
        --repo_3
        Pipfile.lock
    --sub_part_2
    --sub_part_3
    --docker-compose.yml

I have to create a Dockerfile and a docker-compose.yml to run the app.py (flask app) and expose it on a given port

What I have now is

Dockerfile

FROM python:3.8-slim-buster as base

ENV LANG C.UTF-8
ENV LC_ALL C.UTF-8
ENV PYTHONDONTWRITEBYTECODE 1
ENV PYTHONFAULTHANDLER 1
ENV PYTHONUNBUFFERED 1
ENV FLASK_APP subpart_1/repo_2/app.py
ENV FLASK_RUN_HOST 0.0.0.0


RUN pip install pipenv
RUN apt-get update && apt-get install -y --no-install-recommends build-essential libpq-dev gcc musl-dev
COPY ./subpart_1/Pipfile /subpart_1/Pipfile
COPY ./subpart_1/Pipfile.lock /subpart_1/Pipfile.lock

WORKDIR /subpart_1
RUN PIPENV_VENV_IN_PROJECT=1 pipenv install --deploy --ignore-pipfile --sequential
WORKDIR /
COPY ./subpart_1/repo_2 /subpart_1/repo_2/
COPY ./subpart_1/repo_1 /subpart_1/repo_1/

ENV PYTHONPATH /subpart_1/

WORKDIR /subpart_1

EXPOSE 5000
CMD ["flask", "run"]

and the docker-compose.yml

version: "3.9"
services:
  web:
    build: subpart_1/repo_2/
    ports:
      - "5000:5000"

But when I go in my main_project directory and run docker-compose up I have

failed to compute cache key: failed to walk /var/lib/docker/tmp/buildkit-mount585608421/subpart_1: lstat /var/lib/docker/tmp/buildkit-mount585608421/subpart_1: no such file or directory
ERROR: Service 'web' failed to build : Build failed

>Solution :

It seems to me that’s a path issue.

When setting subpart_1/repo_2/ in your docker-compose build file, the build will be done in this repertory. Docker will see the following files:

-app.py
-Dockerfile

thus the copy ./subpart_1/Pipfile /subpart_1/Pipfile cannot work.

I think the easiest way is to put:

version: "3.9"
services:
  web:
    build: 
      context: .
      dockerfile: sub_part_1/repo_2/Dockerfile
    ports:
      - "5000:5000"