Jungles
Without even thinking about scale counts, head shape, or anything else, the body patterning between both is worlds apart. Just look at any adult pygmy and it hardly has any pattern at all or at best an ill defined one.
Adult Stimsons on the other hand always have distinct blotch like patterning and of course the classic lateral line on the anterior third of the body. The confusion that some people have in the wild is picking between hatchlings of the two species because baby pygmys are bolding marked. Their patterns are far more like a childrens python though and their pattern blotching on their lower flanks bordering the ventrals are far more numerous and much smaller in size (unlike a Stimsons). Also juvenile pygmy's usually look far more orange but this can vary depending on locality.