3-4 weeks is a long break between feedings. I mean they'll live, but it isn't recommended. I think a general rule of thumb is every 5-10 days depending on the size of the animal versus the size of the food, your animal's preferred schedule, and your preferred schedule.
Isn't it the huge snakes such as adult Retics , Burms and Boas ( to a lesser extent ) that you can feed every 3 weeks or so ?!