Given $\tau\in H$ (up-half plane) and $q=e^{2\pi i \tau}$, Weber polynomail is defined as

$$f(\tau)=q^{-\frac{1}{48}}\prod_{i=0}^{\infty}(1+q^{i-\frac{1}{2}}).$$

My question is: How can I compute a product of unlimited sequence? Anyway, I have to finish $f(\tau)$ in finite steps. Of course, the faster the better.