ImportError: No module named arcpy

Error Message

When attempting to import arcpy using 64-bit Python that comes with an ArcGIS Server installation, the following error message appears:

Error: 
"ImportError: No module named arcpy"

Cause

The arcpy module's location probably is not specified correctly within the Server10.x.pth file. This file is in the following location:

 <install-drive>\python27\Lib\site-packages

Solution or Workaround

1. Ensure that the following locations are specified in the Server10.3.pth file (the version of ArcGIS Server determines the name of the .pth file):

C:\Program Files\ArcGIS\Server\arcpy
C:\Program Files\ArcGIS\Server\bin
C:\Program Files\ArcGIS\Server\ArcToolbox\Scripts

C:\Program Files\ArcGIS\Server10.3\arcpy

2. From the main toolbar in ArcMap, open the Python window and run the following commands:

>>> import sys
>>> print sys.path

3. Verify that arcpy is in the system path.

['', u'c:\\program files\\arcgis\\server\\arcpy', 'C:\\windows\\system32', 'C:\\Python27\\ArcGISx6410.3\\Lib\\idlelib', 
'C:\\windows\\system32\\python27.zip', 'C:\\Python27\\ArcGISx6410.3\\DLLs', 'C:\\Python27\\ArcGISx6410.3\\lib', 
'C:\\Python27\\ArcGISx6410.3\\lib\\plat-win', 'C:\\Python27\\ArcGISx6410.3\\lib\\lib-tk', 'C:\\Python27\\ArcGISx6410.3', 
'C:\\Python27\\ArcGISx6410.3\\lib\\site-packages', 'C:\\Program Files\\ArcGIS\\Server\\bin', 
'C:\\Program Files\\ArcGIS\\Server\\ArcPy', 'C:\\Program Files\\ArcGIS\\Server\\ArcToolBox\\Scripts']

Python checks both 'sys.path' and the 'Server10.3.pth' file for a module named 'arcpy' when importing arcpy. As long as the location of arcpy is specified, importing arcpy is successful:

>>> import arcpy
>>>

Note:
Python 3 is installed in the latest ArcGIS Server to the following location by default: C:\Program Files\ArcGIS\Server\framework\runtime\ArcGIS\bin\Python\Scripts\propy.bat. Refer to ArcGIS Server: ArcGIS Server and ArcPy. Alternatively, refer to Problem: Unable to use the ArcPy module for more information on the issue.