You can put a hatchling snake in there no problems. Sure it will hide in a little hide but hey why would you want it to do what it does naturally?
As far as I have gathered there have been no studies done to show that a python stresses out in a larger enclosure. You will find keeping them in a larger cage is beneficial not only because it seems to increase muscle tone (only going off my personal experiance) but they seem more 'lively.' Obviously larger breeders keep hatchlings in small plastic tupperwares but that is purely for conveniance and low cost.
EDIT: I keep hatchies in tubs only for conveniance but i do use larger tubs (ie 10L at the least)