This. Sexing by palpation is doable-ish in ball pythons, but the window for doing it is pretty narrow. It's really from about a hatchy to ~200 grams that I can kind of tell a difference between make and female babies, then females develop what feels more or less exactly like the "speed bump." Up until then, male tails feel squishy and then solid; female tails feel solid all the way down.
But it's not reliable. Popping or probing are the ways to go, as Deborah said.