fc = 'TEST.russellpythonguidtest' rows = arcpy.UpdateCursor(fc) for row in rows: row.PYTHONGUID = row.GlobalID rows.updateRow(row)Here is an option if you want to have a GUID that is unique from the GlobalID.
import uuid fc = 'TEST.russellpythonguidtest' rows = arcpy.UpdateCursor(fc) for row in rows: row.PYTHONGUID = '{' + str(uuid.uuid1()) + '}' rows.updateRow(row)