Please enlighten me about PyPy

[Luis M. González]

Hmmm... I know it's complicated, and all these questions can make your
head explode.
I'll tell you what I understand about Pypy and, at the same time, I'll
leave the door open for further explanations or corrections.

As you know, python is a dynamic language.
It means, amongst other things, that the programmer doesn't provide
type information when declaring variables, like in statically typed
languages.
Its code doesn't get translated to machine code through a compiler,
like in C.
Instead, it is "interpreted" by the interprter, which finds out each
variable type at run-time.
This interpretation makes scripting languages like python much slower
than traditional static languages.

Recently, Python got a speed boost via Psyco, which is something like a
proof of concept for a just-in-time compiler. It is a cpython extension
and it can improve python's speed by analyzing run-time information and
generating machine code on the fly.
However, psyco can only analize python code and as you know, python
relies on many extensions coded in c, for performance.
So its author decided that having a python implementation written in
python would laid a much better basis for implementing psyco-like
techniques.

This implementation requires a minimal core, writen in a restricted
subset of python called "rpython". This subset avoids many of the most
dynamic aspects of python, making it easier to authomatically translate
it to C through a tool that uses top-notch type inference techniques.
This translated version of the rpython interpreter (which got already
auto-translated to c), is the basis of Pypy.

On top of it, New Psyco-like and just-in-time techniques will be
implemented for achieving maximum performance.

However, I still doubt that I really understood it...
I'm still not sure if the type inference techniques will be used to
improve the performance of programs running on pypy, or if these
techniques were only intended for getting the rpython interpreter
translated to c.

As far as I know, pypy is currently about 10/20 times slower than
cpython, although many optimizations remain to be done.
And I 'm not sure, but I think that its developers rely on the
psyco-like techniques to achieve the big speed boost their looking for.

Luis