ONE holster TWO guns.

some of the generic nylon ones, like Uncle Mike's will serve for both. But, in general they'll just do a poor job for both.

Virtually any holster made for one will work for the other. They are very closely dimensioned. I'd strongly recommend you get a good quality, fitted leather holster, rather than trust your expensive sixguns to a $15 nylon holster.

well fitted holsters always a good investment, yes, but if these guns be "stars without makeup" used in the brush for chasing bambi and boss hawg, nothing real wrong with a well made cordura holster that fits both, a shoulder rig or chest cross draw perhaps

I don't much do OWB myself, but one of my favorites is a suede lined cordura OWB that fits a SS model 60 snubby real well. I have not seen such in the retail stores around here in a very long time though; apparently not a real popular choice.

I really ought get me some real nice BBQ leather "one of these days". Just too many overdue on my to-do list, never have yet.
If I was handling some of those "stars WITH makeup" six guns that Craig shoots, I would want some custom fit, pretty, soft, fancy leather gloves just to handle 'em !
beautiful stuff

Many holsters will fit both of those two guns, because they are very close to the same size.

The frame, cylinder and barrel dimensions between the two revolvers are very close, so in general terms they should fit the same holsters. One thing you do need to watch for is the thumbbreak strap (if you wish to use one). The Python's hammer spur is longer than that of the 686. A "Jordan" or "Threepersons" type holster has a long, snap-down safety strap and should work with either gun.

I have both a 686 and a Python. Both have 4 inch barrels. I have a Bianchi Shadow and a Bianchi paddle holster marked for the 686. Both holsters work with either revolver. I imagine most quality holsters that fit one would most likely fit the other.

A Tex Shoemaker PC Hugger will work for both of them.

El Paso Saddlery's "Crosshair" will interchange. Top quality and affordable.

I've got a couple of Detective Specials and a couple of J Frame S&Ws. They interchange well with the El Paso Saddlery "Street Combat".

You wont find difficulty in finding a single holster that will work for both.