It is a guard against a stack overflow, yes. Python (or rather, the CPython implementation) doesn’t optimize tail recursion, and unbridled recursion causes stack overflows. You can check the recursion limit with
import sys print(sys.getrecursionlimit())
and change the recursion limit with
but doing so is dangerous — the standard limit is a little conservative, but Python stackframes can be quite big.
Python isn’t a functional language and tail recursion is not a particularly efficient technique. Rewriting the algorithm iteratively, if possible, is generally a better idea.