I had Anaconda 3 installed on my system and python registered with the following link:


I recently updated some libraries in Anaconda 3 and then ExternalEvaluate and ExternalLanguage cell stopped working giving the following error.

StartExternalSession::noinstall: No valid installations for system Python were found with the options specified.

So I cleared the cache of the ExternalEvaluate using the following command: ExternalEvaluate`Private`resetCache[]

and attempted to register again:


giving the following weird error:

RegisterExternalEvaluator::invalid: -- Message text not found -- (ExternalEvaluate`Private`reason)

I rebooted my computer but nothing is fixing the issue. Please help.

  • 1
    $\begingroup$ Make sure you follow the instructions here and have zmq installed. $\endgroup$ – Szabolcs Feb 12 at 18:34
  • $\begingroup$ Found out the issue. After downgrading to version 3.6.7 using conda install python = 3.6.7, it worked again. Since I did installed new libraries and did a general update it updated my python version to 3.6.8 which is not working with ExternalEvaluate (mathematica 11.3). Maybe it will be supported from 12.0 onwards. $\endgroup$ – user13892 Feb 12 at 18:38
  • $\begingroup$ Hmm ... M11.3's ExternalEvaluate seems to work fine for me with Python 3.7.2 installed through Anaconda. $\endgroup$ – Szabolcs Feb 12 at 18:41
  • $\begingroup$ It all works for me with python 3.6.8 and 11.3. $\endgroup$ – b.gates.you.know.what Feb 12 at 21:34
  • $\begingroup$ when you do conda update python what version of python it is showing as the latest? Maybe because I have an older version of anaconda. $\endgroup$ – user13892 Feb 12 at 21:42

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