How fast is PyPy?
In three words, PyPy is “kind of fast”. In more than three words, the answer to this question is hard to give as a single number. The fastest PyPy available so far is clearly PyPy with a JIT included, optimized and translated to C. This version of PyPy is “kind of fast” in the sense that there are numerous examples of Python code that run much faster than CPython, up to a large number of times faster. And there are also examples of code that are just as slow as without the JIT. A PyPy that does not include a JIT has performance that is more predictable: it runs generally somewhere between 1 and 2 times slower than CPython, in the worst case up to 4 times slower. Obtaining good measurements for the performance when run on the CLI or JVM is difficult, but the JIT on the CLI seems to work nicely too.
