Once you&#x27;ve exhausted all the low-hanging fruit, like people calling .keys() on dicts, or doing unnecessary linear searches, Cython really starts to shine. I&#x27;ve seen it perform ~40 times better than pure Python in time-consuming loops.<p>We do scientific computing at my company. Numpy does 90% of the work, but there are some algorithms that just aren&#x27;t easily expressed with arrays. That&#x27;s where Cython comes in.