I'm just trying out ArcGIS Pro for the first time and I had to change my PYTHONPATH to python34

ArcGIS Pro is now working without crashing every time I open the Analysis tab... However now when I try to run a process in ArcMap 10.3.1, I get various python errors; on tools that worked a half hour ago with the same exact data inputs.

Is this a conflict in python versions since ArcGIS 10.3.1 uses 2.7?

Is there a way to have ArcGIS Pro and ArcGIS 10.3.1 running simultaneously on the same machine, even though each utilizes a different python version?

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  • 1
    I have both installed on my PC, no errors. I did not change PYTHONPATH.
    – klewis
    Commented Jan 29, 2016 at 15:54
  • How do you not encounter issues when selecting the Analysis tab in ArcGIS Pro? It will crash if the PYTHONPATH is not pointed to python34...
    – LMHall
    Commented Jan 29, 2016 at 15:55
  • ArcGIS Pro 1.1 I just changed the PYTHONPATH back to C:\Python27\ArcGIS10.3\Lib\site-packages and my processes in ArcMap 10.3.1 are running fine... Now my ArcGIS Pro is crashing again on Analysis Tab.
    – LMHall
    Commented Jan 29, 2016 at 16:11
  • I'll try to reinstall ArcPro 1.1
    – LMHall
    Commented Jan 29, 2016 at 16:20
  • Dont think that'll 'fix it'. Im waiting to hear from a co-worker on this
    – KHibma
    Commented Jan 29, 2016 at 16:33

1 Answer 1


I'll try to explain this the best I can so hopefully you can move forward. The short answer is, if your PYTHONPATH is pointing at an actual version of Python, when a product loads up and needs Python it's going to see this directory. In the case of ArcGIS Pro (64bit, using Python 3.4) and ArcMap (32bit, using Python 2.7)... well the use of PYTHONPATH and pointing to the 'wrong' version of Python is going to break the application. (wrong and break is based on where you're pointing at and what app you load) Ie. Your system wide level of saying "import these modules for any/all versions of Python!" is what confuses/breaks ArcGIS.

How to use PYTHONPATH explains PYTHONPATH better than I can.

The question is why do you need the PYTHONPATH? What application wants this? If you take a look here C:\Python27\ArcGIS10.3\Lib\site-packages you'll see .pth files. These are used at the particular Python version to point at required modules. Could you make use of a .PTH for the particular version of Python that has required you to plug in the PYTHONPATH to begin with?

  • Not sure what happened, I just reinstalled ArcPro and reset the PYTHONPATH to the default for ArcGIS 10.3.1 Both seem to be working now again... Time will tell?
    – LMHall
    Commented Feb 17, 2016 at 19:27
  • what do you mean default? ArcGIS install doesnt set a PYTHONPATH
    – KHibma
    Commented Feb 17, 2016 at 20:21
  • It certainly did for me... PYTHONPATH - C:\Python27\ArcGIS10.3\Lib\site-packages
    – LMHall
    Commented Mar 2, 2016 at 19:38

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