streamlit's webserver not working when using pdm for installation

Summary

When I’m using pdm to install streamlit, I cannot connect to streamlit’s webserver. From pdm’s web site: PDM is a modern Python package manager with PEP 582 support.

Steps to reproduce

1. Install PDM: pipx install pdm
2. Create new directory and go there: mkdir st_test; cd st_test
3. Init pdm: pdm init (and use the defaults)
4. Install streamlit: pdm add streamlit
5. Use any minimal streamlit example and run streamlit: pdm run streamlit run hello_world.py

Expected behavior:

Browser opens correct web page served by streamlit.

Actual behavior:

Browser tries to connect to localhost:3000 (which is also mentioned in the logs), but when I look at the logs, the server actually runs on port 8501. When I try this port, I get a 404, so I can connect to the server on this port, but something’s broken.

Is this a regression?

That is, did this use to work the way you expected in the past? never tried before

Debug info

• Streamlit version: 0.80.0
• Python version: 3.8.8
• Using pdm
• OS version: Linux 5.11.11
• Browser version: Chrome 89.0.4389.114 (Official Build) (64-bit)

Additional information

jupyter-lab show a similar issue with pdm, but it can be fixed by running pdm run jupyter-lab --core-mode

[randyzwitch]

It looks like @AnOctopus is an enthusiast and is working towards this:

https://github.com/pdm-project/pdm/issues/972

I’ll re-open, so everyone can be aware that its been requested.

[AnOctopus]

I found a way that works: pdm-project/pdm#989 (comment). Hopefully it’s not only for me, but for everyone.

Actually PDM is getting more and more popular recently. It would be great if it could be supported officially.

That workaround gives me a very good idea about the source of the problem. We automatically set development mode by trying to detect how streamlit was installed, and I suspect being installed into __pypackages__ breaks our heuristics for that. Should be relatively easy to fix.