Python tail-recursive

gistfile1.py

class tail_rec:
    inside = False

    def __init__(self, func):
        self.func = func

    def __call__(self, *args, **kwargs):
        if tail_rec.inside:
            self.args = args
            self.kwargs = kwargs
            return self
        try:
            tail_rec.inside = True
            r = self.func(*args, **kwargs)
            while isinstance(r, tail_rec):
                r = r.func(*r.args, **r.kwargs)
            return r
        finally:
            tail_rec.inside = False

@tail_rec
def factorielle(n, acc=1):
    if not n:
        return acc
    return factorielle(n - 1, acc * n)

print(factorielle(5000))