After upgrading to ArcGIS 10.4, i am now get an runtime error when importing arcpy into 64bit Python Idle. 32bit works just fine and 64bit works unless i import arcpy library. Please see the below:
arcmap is still 32 bit and was that the version installed by arcmap? if not, there is no real reason to have a slightly newer version of 2.7.* installed. Install ArcGIS PRO and work with python 3.4 (albeit only a few years out of date)
If you want to complicate matters, you can examine the difference between 32 and 64 bit with respect to foreground and background geoprocessing Background Geoprocessing (64-bit)—Help | ArcGIS for Desktop
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