Guidelines to write fast code for PyPy's JIT

Question

PyPy's JIT can make Python code execute much faster than CPython. Are there a set of guidelines for writing code that can be optimised better by the JIT compiler? For example, Cython can compile some static code into C++, and it has guidelines to write efficient code. Are there a set of good practices for PyPy? I know that the PyPy project has guidelines for including hints while writing your own JIT-enabled interpreters for other dynamic languages, but that is not relevant to most end users of the framework, who are simply using the interpreter. Questions I am wondering about include:

1. Packaging a script into functions
2. Explicitly deleting variables
3. Possible ways of giving, or hinting variable types
4. Writing loops a certain way

Answer 1

PyPy wiki's at BitBucket has a section on JIT Friendliness. Some blog posts offer further advice on making code run fast in PyPy, but AFAIK the idea is that idiomatic code that doesn't force interpreting/realizing frames should be fast and is a bug if it isn't.

I know that for 3, some "assert x > 0" or similar statements can be useful, but I don't remember where I saw that. I also believe I've seen some suggestion about refactoring conditional-paths-in-loops related to 4 (edit: this seems to be outdated now).

Here's a thread with some related discussion. You can check how well the JIT is working with your code with jitviewer, but it's somewhat advanced. Joining #pypy on Freenode will get you help with jitviewer and your particular code.