fibonacci.py

cpdef int fib(int n):
    
    cpdef fibAux(int n, int a, int b):
        if n == 0:
            return a
        else:
            return fibAux(n-1,a+b,a)
            
    if n == 2 or n == 1:
        return n
    elif n > 0:
        return fibAux(n,0,1)  
    else:
        raise ValueError('Fibonacci need be a natural number.')

if __name__ == '__main__':
    print(fib(992))

Here, you can see Fibonacci with tail-call recursion.
It allows the compiler to do tail-call optimization and don't blow up
the call stack when dealing with deep recursions.