A ball python will not strike "for no apparent reason," if it strikes, it feels threatened or perceives something as food. Even if you know your ball python's personality and you have never had an unpleasant interaction, you could do something as simple as make a sudden move that surprises it and it could instinctively strike defensively.

I personally do not let my girl near my face. Yes, I trust her and she has never bit me, but she doesn't need to be near my face for any reason. I let her crawl up my arms, but if she gets to close, I just very gently guide her elsewhere. A reptile is not a good thing to have near your face for sanitary reasons as well, they are carriers of salmonella, just a fact, so any part of your body that they touch should be washed immediately afterwards. Just because I have a reptile in my tiny apartment and I change her water in the sink, I do not wash any dishes by hand and I bleach the sink and counters every day, several times a day. Just common sense.

Ball pythons make great pets because they generally are not biters, but any snake can and will bite if it sees a reason to, and its reasoning may make no sense to you. All snakes should be respected, and when any of us get bit, it's our mistake, not the snake's. We are a lot bigger than our ball pythons, so they have every reason to be fearful of us. It is about getting them to trust US, not the other way around.