[Python] Why does running a Dockerized Python app with uv run trigger a build while it doesn't...

Disclosure: I'm currently learning how to use the uv package manager as well as, concurrently, Docker.

Say my folder structure is:

my_project/
├── src/
│ └── __init__.py
│ └── utils.py
│ └── hello_world.py
├── pyproject.toml
├── README.md
├── uv.lock


In order to call src as a package I configured my pyproject.toml the following way:

[project]
name = "project-name"
version = "0.1.0"
description = "project-description"
authors = [
{name = "my-name", email = "my@email.com"}
]
dependencies = []

readme = "README.md"
requires-python = "==3.12.*"

[build-system]
requires = ["setuptools>=61.0"]
build-backend = "setuptools.build_meta"

[tool.setuptools]
packages = ["src"]


This way I can call some functionality of the utils.py file in the hello_world.py file like:

from src.utils import print_hello_world

print_hello_world()


I then tried to 'dockerize' my simple app. The Dockerfile is:

# Use a Python image with uv pre-installed
FROM ghcr.io/astral-sh/uvython3.12-bookworm-slim

WORKDIR /app

ADD . /app

RUN uv sync

ENTRYPOINT [ "uv", "run", "src/hello_world.py" ]


I then built the image with docker build -t myimage . And ran it with docker run myimage.

For some reason whenever I run the image uv builds my project before printing the "Hello, world!" message.

user@host:~/projects/my-project$ docker run -it myimage:latest
Built project-name @ file:///app
Uninstalled 1 package in 4ms
Installed 1 package in 3ms
Hello, world!


However, if I do the same steps detailed in the Dockerfile but on my machine no 'build' stage seems to take place whenever I run my file with uv run. E.g.:

user@host:~/projects/my-project$ uv lock
Using CPython 3.12.0
Resolved 1 package in 0.71ms
user@host:~/projects/my-project$ uv sync
Using CPython 3.12.0
Creating virtual environment at: .venv
Resolved 1 package in 0.71ms
Installed 1 package in 52ms
+ project-name==0.1.0 (from file:///home/fmppo/projects/so-question)
user@host:~/projects/my-project$ uv run src/hello_world.py
Hello, world!


Could you help me understand why this is happening?

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