This is the 50mm standard lens that come with my Ricoh KR-5 Super. However, it seems that the camera had also been sold with an non-XR version of this lens (see photo in Camera-wiki entry: http://camera-wiki.org/wiki/Ricoh_KR-5_Super). There is also an non-L version of this lens (see https://www.pentaxforums.com/userreviews/ricoh-xr-rikenon-50mm-f-2-0.html) which focuses down to 0.44m instead of 0.6m and has a metal lens body (so “L” could mean “light”). To confuse you more, a “P” version (like the SMC-A of Pentax) was also made for Ricoh bodies with progranmmed auto and shutter-priority modes. However, this “P” version is incompatible with most K-mount bodies and forcing one on risks damaging the body.
Back to the lens itself, it is a non-P Ricoh lens and thus has a standard fully mechanical Pentax-K mount which will fit on almost all Pentax bodies even for the DSLRs. The only concern would be Whether your body can meter with the lens or not. The focusing mechanism is not as good as my Pentax SMC-A 50mm f2. It is smooth but there is not enough friction. My only real complaint about this lens is it does not have half-stop clicks on the aperture ring. However, optically this lens outperform the Pentax although some might think the bokeh of the Pentax is “nicer” than the Ricoh. How about a sample shot? Below was taken with Ilford HP5+ exposed at ASA200 using the XR Rikenon 50mm f2 L mounted on my ME Super.