Sure. Stefan's right. You can judge by the relative length of the tail, but it's most reliable when you're comparing two snakes of the same age or size. Otherwise, you have to rely on judgement and memory
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My initial impression that it might be a male was because I don't see a real dramatic change in the width/depth of the tail right before and after the vent. It seems pretty straight with only a little change. I'm also guessing that your snake is fairly young and small, like an adolescent, based on its diameter and the diameter of your fingers. Adolescents can also be tricky to judge, and like Don said, you can't pop them at that stage.
Rick