The pictures are rather bad to be able to tell what it is -- it looks to me like scarring likely from trying to squeeze himself through something that ripped the top off him or his food chewed on him. Aside from better pictures you might want to take him to a vet to have him looked at -- if it's an old scar then it won't likely clear up -- if it's something fresh then it might be treatable.

Good luck with him!
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Tosha
JET Pythons

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