file geodatabase - Setting default gdb from ArcPy?

I created a new gdb by

arcpy.CreateFileGDB_management('e:/Rstack', 'new.gdb')
arcpy.env.workspace = 'e:/Rstack/new.gdb'

But how to set this new gdb as my default gdb by arcpy, without opening ArcGIS desktop? Setting env workspace does not seem to work here.