The sys.path.append method

The sys.path property is a mutable list, and can be appended or extended to include new file paths that will point to modules the user wants to import. To avoid the need to adjust the sys.path, copy the module into the site-packages folder; however, this is not always possible, so use the sys.path.append method as needed:

>>> sys.path.append("C:\\Projects\\Requests")
>>> sys.path
['', 'C:\\WINDOWS\\SYSTEM32\\python27.zip', 'C:\\Python27\\ArcGIS10.5\\Dlls', 'C:\\Python27\\ArcGIS10.5\\lib', 'C:\\Python27\\ArcGIS10.5\\lib\\plat-win', 'C:\\Python27\\ArcGIS10.5', 'C:\\Program Files (x86)\\ArcGIS\\Desktop10.5\\arcpy', 'C:\\Program Files (x86)\\ArcGIS\\Desktop10.5\\ArcToolbox\\Scripts','C:\\Projects\\Requests']  

When the sys.path.append method is used, the adjustment is temporary. Adjust the PYTHONPATH environment variable in the Windows System Properties menu (discussed earlier in the Path environment variable section) to make a permanent change (and create the PYTHONPATH if it has not been created).

One last, valuable note: to import a module without adjusting the system path or copying the module into the site-packages folder, place the module in the folder that contains the script that is importing it. As long as the module is configured correctly, it will work normally. This is useful when there is no administrative access available to the executing machine.