Just a note: Any holster that is built for the Colt Python will fit the L-frame. I am working on a magazine article about this and a couple of months ago I snapped photos to demonstrate it.
Dave: The S&W L-frame is very similar in profile and overall dimensions to the Colt Python, as well as the Ruger GP100, however they are not identical. A number of differences will be found upon close examination and measuring.
Many manufactured holsters made for these revolvers will accept them all interchangeably. Hand-made holsters that are closely formed for one model may not provide the same result. In any event, those small differences can manifest themselves in differing performance and greater tendencies to cause holster wear to the revolver finish.
The most common problem that seems to rear its head is the differences in hammers, particularly with holsters featuring thumb-break retention. A thumb-break made to fit the L-frame hammer will not work at all with the Colt Python's long target hammer. A thumb-break holster made for the Colt Python's hammer, when used with the L-frame (or GP100) will allow considerable movement of the revolver within the holster, and the thumb-break may not be entirely reliable in function.
When the L-frame revolvers were first introduced (about 1980 as I recall) there simply were no holsters made specifically for it, and the new owners found that holsters made for the Colt Python provided a ready option.
For those pursuing the best possible fit and function a holster formed specifically for the intended revolver is the best choice. For those willing to accept something less than perfect a holster made for any one of these may provide some level of utility with all the others.
