New answers tagged 64bit
The download for the 64 bit geoprocessing installation is not freely available. I found it in my.esri.com under My Organizations -> Downloads -> ArcGIS for Desktop 10.4 -> ArcGIS for Desktop Background Geoprocessing (64-bit).
If you only have access to ArcGIS Desktop or Engine, you need to install the Background Geoprocessing for 64bit, check this page. If you have ArcGIS Server, the 64bit Python will be automatically installed. A Help page on that: What is 64-bit Background Geoprocessing?
check out this link, http://support.esri.com/fr/knowledgebase/techarticles/detail/40838 it fixed my problem. Easier than working with environment path, you can just call the python path (32bit) in c\python27\arcgis folder in command line to pass the path to .py file.
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