Your snake has limited vision right now due to being in shed. It can't see to you as well. Your movement is probably a shadowed blur, so it doesn't know what you are. That's why it's hissing.
Just wait to handle your snake when it's done shedding.
Even if your snake was a regular hisser, it's really nothing to worry about. Some are just more 'talkative' than others.
None of my adults hiss, but some of them hissed a boat load when they were youngsters. It's normal for babies to hiss. They're vulnerable at that age.
And I rarely handle my snakes regularly. The only time I really handle them is to clean their enclosures. Never had to worry about them becoming not 'hand trained' because they don't really need the 'training' to begin with. They're a very tame docile species in general from the get go. (aside from the very rare exception)
Not to mention that bites from ball pythons do not hurt. They are surprising, yes. But a paper cut hurts worse, in my opinion.I've been bitten a few times and I really didn't know I was hit until I saw the blood. Didn't feel a thing.
And a ball python usually only bites out of fear or insecurity. Hardly ever from true aggression. So as long as it feels safe and you don't smell like a feeder, there is a very slim chance of you actually getting bitten.