Generally mature ball pythons (meaning, not a baby or juvie) will go off feed during the breeding season, which can be any time between Oct/Nov through May/June.
It's unusual for a baby or juvenile to go off feed during the winter months, because they are hard wired to grow more quickly (in the wild, being small makes you a target to predators, so growing quickly is advantageous to them). If a younger ball python goes on a fast, 99% of the time, it's husbandry related, and our caresheet has a great portion called "why won't my snake feed?" that gives the novice keeper a list of items to check to make sure they are not the "trigger" for the fast.
If a mature adult goes off feed in the winter months, most of the time, it can be contributed to seasonal fasting.
Also, smaller meals on a weekly basis can help to keep your snake feeding consistently year round. Most of my refusals are with females who have been paired with males and are nearing ovulation. The rest of my ~40 ball pythons feed year round.