Rpy2 does not work with streamlit

Summary

One can not use the package Rpy2 to call R function from within streamlit. Importing the rpy2 package crashes with an “ValueError: signal only works in main thread”

Steps to reproduce

Code snippet:

import streamlit as st
import rpy2.robjects as robjects

Expected behavior:

Importing the rpy2 package

Actual behavior:

Importing the rpy2 package crashes with an “ValueError: signal only works in main thread”

Is this a regression?

Do not know, never tried before.

Debug info

• Streamlit version: 0.74.1
• Python version: (3.8
• Using Conda
• OS version: Ubuntu 20
• Browser version: Chrome 87.0.4280.141

Additional information

I was told to open this issue in the discussion forum, see https://discuss.streamlit.io/t/using-rpy2-within-streamlit/8812

[lgautier]

Otherwise I don’t think that there is any reason R would (or could) keep running after the Python process ends. R is embedded in the Python process. Think of it as a C library called from the Python process.

[lgautier]

I am not familiar enough with Streamlit, but I suspect that importing streamlit has side effects (beyond loading Python modules and packages). One of them is that one or several threads are created and the rest of the code in your Python module (that is source file) will be evaluated by the thread(s).

If the case, changing the order of imports might clear the warning message you are seeing. Try changing

import streamlit as st
import rpy2.robjects as robjects

to

import rpy2.robjects as robjects
import streamlit as st