Evaluate Ankermann Function using Python

The Ankermann function, A(m, n) is defined as

The Python code below could be used to evaluate the Ankermann function.

def ack(m,n):
    if m == 0:
        return n+1
    elif m > 0:
        if n == 0:
            return ack(m-1, 1)
        elif n > 0:
            return ack(m-1, ack(m, n-1))

Usage:

ack(3, 4)

However, this code can't be used for larger values of m and n.