Is it normal for a Ball Python to try biting while you're holding it?

I recently adopted a Ball Python from an exotic animal rescue. I've had multiple snakes over the years, 3 of which were ball pythons (male), so I usually know what's normal and what isn't. This new animal is keeping me on my toes! It's about 3ft, and I'm not sure about male or female because the woman running the rescue didn't know, and I can't handle him without getting attacked. I've had him/her home for a week and fed it 2 medium rats in that time, so I don't think he's snapping because he's hungry, and he shed right before I adopted him. I'm well aware that pythons can snap when you leave your hands it their tank, but is it normal for them to snap while you're holding it? The first time I went to hold him since bringing him home he went nuts! I had him about 2 inches below his head, so he couldn't reach to turn and bite... he actually tried a back-bend maneuver to go after me! What's the deal? I'm wondering if it's really a she, and she's gravid- therefore aggressive. I know she was being kept with two other male pythons for several weeks before I picked her up, but it's kinda early in the year I think... Advice?