For some reason, diadem ratsnakes, sometimes called Egyptian ratsnakes, have become common in the pet trade. These are not true ratsnakes, which would be in the genus Elaphe, but rather are in the genus Spalerosophis. I've had several of these snakes, and currently have a pair of sub-adults.
These snakes are very easy to keep in captivity. They can be kept like Elaphe or Lampropeltis, requiring only a decent-sized cage, simple substrate, water, weekly feedings, and heating at room temperature. Because they can be heavy-bodied as adults, they don't require climbing branches. While my largest adults were about 4 feet long, the maximum length is probably longer than that. Adult coloration can be very attractive, a salmon-orange background with black blotchings around the head and neck region. These snakes come from Northern Africa through the Middle East, into India.
As far as personality is concerned, juveniles can be very aggressive. They need constant handling if you want calm adults. I did purchase a pair of adults at the Mid-Atlantic Reptile Show that were very handleable, so I know that they can be tamed down. Aggressive displays include hissing and puffing up their bodies, as well as striking and biting. Bites from juveniles are hardly worth mentioning, although I've noticed a tendency to chew.
There appear to be several forms of Spalerosophis in the pet trade. I don't know whether these are all subspecies of S. diadema, or include other species in the genus. The only paper I've come across on the topic lists three species in the genus, and four subspecies of S. diadema. The paper may be out-of-date, so if anyone has an updated review, please let me know.
Marx (1959) lists the following:
Spalerosophis microlepis - Mid-body scale rows are 41 or more
Spalerosophis arenarius - 35 or less mid-body scale rows, rostral very long and wedged between internasals (though not completely seperating them)
Spalerosophis diadema - 35 or less mid-body scale rows, rostral is not very long
Spalerosophis diadema diadema - irregular dorsal markings, usually over 100 subcaudals
Spalerosophis diadema dolichosphila - has unique large, uniform, oval dorsal spots
Spalerosophis diadema cliffordi - irregular dorsal markings, less than 80 subcaudals
Spalerosophis diadema schiraziana - irregular dorsal markings, 80-100 subcaudals
S. microlepis is only known from Iran, so probably does not enter the pet trade. S. arenarius comes from India and Pakistan. Most of the Spalerosophis in the pet trade are probably diadema, which covers most of the known range of Spalerosophis, and are probably S. d. diadema and S. d. cliffordi. S. d. diadema is known to have several color varieties, including one that is sometimes referred to as S. d. atriceps (but should probably just be considered a synonym for S. d. diadema.)
Marx, H. 1959. Review of the colubrid snake genus Spalerosophis. Fieldiana Zoology (Chicago Natural History Museum) 39(30): 347-361.