According to researcher Chuck Hansen, the W34 Python was a gas-boosted fission primary used in several designs of American thermonuclear weapons.
Hansen's research indicates that the W34 Python primary was used in the US B28 nuclear bomb, W28, W40, and W49, and as a boosted fission warhead without a thermonuclear second stage in several other weapons.
Peter was also proposed as a replacement for the Red Beard warhead housed in a Red Beard carcass, and as the Violet Mist nuclear land mine for the British Army in Germany.
The W34 used the melt-cast high explosive Octol, a variant of HMX and TNT as the material for its implosion lenses, and this relatively unsophisticated explosive that pre-dated PBX was perhaps a reason why the British adopted this warhead, since they were attempting to deploy a thermonuclear warhead for their strategic bombers quickly, and the British were well-versed in the manufacture, storage and use of these melt-cast explosives.
There is no hard evidence as yet, but the 11 kt yield of the W34 Python would degrade to a figure comparable with the W25 without the gas-boosting.