Module not found when using UV, py-shiny and external dependency

I want to create a shiny app (using py-shiny) where I manage the dependencies using uv.

So far I have used the following code

uv init shiny-tester
cd shiny-tester
uv add shiny
vim app.py # see below
uvx shiny run # works as expected

where I write the following to app.py (directly taken from the official doc):

from shiny import App, reactive, render, ui

# will be used later
# import numpy

app_ui = ui.page_fluid(
    ui.input_action_button("action_button", "Action"),  
    ui.output_text("counter"),
)

def server(input, output, session):
    @render.text()
    @reactive.event(input.action_button)
    def counter():
        return f"{input.action_button()}"

app = App(app_ui, server)

This works as expected using uvx shiny run and the app runs.

When I try to add any other package, eg numpy by inserting a import numpy into app.py, I get the error that the module could not be found because I didnt install it yet. To fix this I run uv add numpy, which works and does not throw any errors.

When I run uvx shiny run however, I still get the error

  File "/mnt/c/Users/david/Desktop/shiny-tester/app.py", line 2, in <module>
    import numpy
ModuleNotFoundError: No module named 'numpy'

When I run uv run python and import numpy the module can be found and loaded.

Any idea what might cause this and how to fix it?

Version etc

❯ uv --version
uv 0.4.17
❯ cat pyproject.toml
[project]
name = "shiny-tester"
version = "0.1.0"
description = "Add your description here"
readme = "README.md"
requires-python = ">=3.12"
dependencies = [
    "numpy>=2.1.1",
    "shiny>=1.1.0",
]

❯ head uv.lock
version = 1
requires-python = ">=3.12"
resolution-markers = [
    "platform_system != 'Emscripten'",
    "platform_system == 'Emscripten'",
]

[[package]]
name = "anyio"
version = "4.6.0"

Solution

uvx is for global tools. uvx sometool installs sometool into a temporary, isolated environment. This means the shiny executable running your app does not have access to your actual environment.

uv run is what you want:

$ uv run shiny run
INFO:     Started server process [11373]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)