OK, you're getting (or have) a Nile and you're worried about a White Lip's temperament? I've had 5 so far, and they are great snakes BUT very high-strung and nervous. It is true that you will run into respiratory troubles if you can't keep up the humidity and the temps. They need frequent misting and temps in the upper 80s. I trick I used to keep the humidity up was to use cypress mulch as bedding, mist the cage heavily each day, and cover the top except for a small corner with a wet towel. The whole room was heated to an even temperature by a centrally located space heater. Final word on this vein, have the name of a good exotic vet in advance because you will be doing business with them.
Regarding temperament, males are more easily manageable than females. Maybe it's just my experience, but I have been bitten only once by a male while I was open season to my 3 females. Their teeth aren't terribly long but wounds from their bites bleed freely so be prepared. Watch your face! Neither sex of this species reacts well to sudden or 'jerky' movements and you will get bitten or they will bash their nose against the aquarium - neither of which is a good thing obviously. In conclusion, please allow me to stress that this is not a good starter snake if you are new to keeping snakes.
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Who is like Set...
1.1 Vietnamese Blue Beauties
2.2 Taiwan Beauties
2.3 Cave Beauties
0.1 Bull Snake
1.0.0 Argentine Blk & Wht Tegu
2.5 Box Turtles