rpy2 throws a NotImplementedError concerning Conversion rules

Question

I'm trying to implement R code inside some Python (3.10) software using rpy2 (3.5.7). I want to know whether I can get rpy2 to work before trying anything complicated. This is an "off-the-shelf" execution, using one of the earliest examples in the documentation introduction. I am running this from inside the PyCharm IDE. There is no mention of performing any prerequisites in the documentation.

There is a slight nuisance to this simple code. It is being executed within an event call (clicking a button) using the DearPyGUI package.

This is the rpy2 code:

import rpy2.robjects as objects
print(robjects.r)

Unfortunately, this throws:

...
    raise NotImplementedError(_missingconverter_msg)
NotImplementedError: 
    Conversion rules for `rpy2.robjects` appear to be missing. Those
    rules are in a Python contextvars.ContextVar. This could be caused
    by multithreading code not passing context to the thread.

This is a working example of the error:

import dearpygui.dearpygui as dpg
import rpy2.robjects as robjects

def testFunction():
    print(robjects.r)

dpg.create_context()
dpg.create_viewport()
dpg.setup_dearpygui()

with dpg.window(label="Example Window"):
    dpg.add_text("Hello world")
    dpg.add_button(label="Save", callback=testFunction)

dpg.show_viewport()
dpg.start_dearpygui()
dpg.destroy_context()

With the full error message:

Traceback (most recent call last):
  File "/home/anthony/CPRD-software/test.py", line 6, in testFunction
    print(robjects.r)
  File "/home/anthony/anaconda3/envs/CPRD-software/lib/python3.10/site-packages/rpy2/robjects/__init__.py", line 451, in __str__
    version = self['version']
  File "/home/anthony/anaconda3/envs/CPRD-software/lib/python3.10/site-packages/rpy2/robjects/__init__.py", line 440, in __getitem__
    res = conversion.get_conversion().rpy2py(res)
  File "/home/anthony/anaconda3/envs/CPRD-software/lib/python3.10/functools.py", line 889, in wrapper
    return dispatch(args[0].__class__)(*args, **kw)
  File "/home/anthony/anaconda3/envs/CPRD-software/lib/python3.10/site-packages/rpy2/robjects/conversion.py", line 370, in _raise_missingconverter
    raise NotImplementedError(_missingconverter_msg)
NotImplementedError: 
    Conversion rules for `rpy2.robjects` appear to be missing. Those
    rules are in a Python contextvars.ContextVar. This could be caused
    by multithreading code not passing context to the thread.

What is going on?

Answer 1

I solved this issue by wrapping all relevant rpy2 code in a context

from rpy2.robjects import conversion, default_converter
with conversion.localconverter(default_converter):
    # rpy2 code here

Conversions happen any time you materialise R objects concretely within python. In this case the print() is causing this to happen.

Working as of rpy2=3.5.11

Answer 2

This is an issue with newer versions of rpy2. I was able to successfully overcome this issue by downgrading:

pip install rpy2==3.5.1