Reticulate: use_python appears to have no effect

[cb4github]

Please excuse my poor or incorrect usage, if any, in the following.

> library(reticulate)
> py_config()
python:         /home/<my id>/anaconda3/bin/python
libpython:      /home/<my id>/anaconda3/lib/libpython3.5m.so
pythonhome:     /home/<my id>/anaconda3:/home/<my id>/anaconda3
version:        3.5.2 |Anaconda custom (64-bit)| (default, Oct 20 2016, 03:10:33)  [GCC 4.8.2 20140120 (Red Hat 4.8.2-15)]
numpy:          /home/<my id>/anaconda3/lib/python3.5/site-packages/numpy
numpy_version:  1.11.2

python versions found: 
 /usr/bin/python
 /usr/bin/python3
 /home/<my id>/anaconda3/bin/python

Attempting to change python version:

> use_python("/usr/bin/python", required = T)

Observe - no apparent change:

> py_config()
python:         /home/<my id>/anaconda3/bin/python
libpython:      /home/<my id>/anaconda3/lib/libpython3.5m.so
pythonhome:     /home/<my id>/anaconda3:/home/<my id>/anaconda3
version:        3.5.2 |Anaconda custom (64-bit)| (default, Oct 20 2016, 03:10:33)  [GCC 4.8.2 20140120 (Red Hat 4.8.2-15)]
numpy:          /home/<my id>/anaconda3/lib/python3.5/site-packages/numpy
numpy_version:  1.11.2

python versions found: 
 /usr/bin/python
 /usr/bin/python3
 /home/<my id>/anaconda3/bin/python
> R.version
               _                           
platform       x86_64-pc-linux-gnu         
arch           x86_64                      
os             linux-gnu                   
system         x86_64, linux-gnu           
status                                     
major          3                           
minor          3.3                         
year           2017                        
month          03                          
day            06                          
svn rev        72310                       
language       R                           
version.string R version 3.3.3 (2017-03-06)
nickname       Another Canoe               
> 

Shouldn't the result of use_python be reflected in the result of py_config()?

Please let me know if you need more info, thanks.

Best,
CB

[cb4github]

> packageVersion("reticulate")
[1] ‘0.7’
> 

[jjallaire]

You can only load one Python interpreter per R session (it can't really be cleanly unloaded without messy side effects that cause crashes down the road) so the use_python call only applies before you actually initialize the interpreter.

[bryanhanson]

To any newbies out there (like me), this means do:

library("reticulate")
use_python("/usr/bin/python", required = T)

Before anything else. Check with

py_config()

[battmanux]

I actually do:

reticulate::use_python("python3")
library(reticulate)

[flying-sheep]

That doesn’t work, you should do

reticulate::use_python(Sys.which('python3'), required = TRUE)

And there’s no difference if you do it before library(reticulate) or after, as long as it’s before you try to run any other stuff.