Maximum recursion depth?

Question

I have this tail recursive function here:

def fib(n, sum):
    if n < 1:
        return sum
    else:
        return fib(n-1, sum+n)

c = 998
print(fib(c, 0))

It works up to n=997, then it just breaks and spits a "maximum recursion depth exceeded in comparison" RuntimeError. Is this just a stack overflow? Is there a way to get around it?

Answer 1

Looks like you just need to set a higher recursion depth

sys.setrecursionlimit(1500)

Answer 2

It's to avoid a stack overflow. The Python interpreter limits the depths of recursion to help you avoid infinite recursions, resulting in stack overflows. Try increasing the recursion limit (sys.setrecursionlimit) or re-writing your code without recursion.

from python website :

---

sys.getrecursionlimit()

Return the current value of the recursion limit, the maximum depth of the Python interpreter stack. This limit prevents infinite recursion from causing an overflow of the C stack and crashing Python. It can be set by setrecursionlimit().

Answer 3

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 change the recursion limit with sys.setrecursionlimit, 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.

Answer 4

Use a language that guarantees tail-call optimisation. Or use iteration. Alternatively, get cute with decorators.