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==========================
Frequently Asked Questions
==========================
.. contents::
General
============================================================
Do I have to rewrite my programs in RPython?
--------------------------------------------
No. PyPy always runs your code in its own interpreter, which is a full
and compliant Python 2.4 interpreter. RPython_ is only the language in
which parts of PyPy itself are written.
I am getting strange errors while playing with PyPy, what should I do?
----------------------------------------------------------------------
It seems that a lot of strange, unexplainable problems can be magically
solved by removing all the \*.pyc files from the PyPy source
tree. Another thing you can do is removing the pypy/_cache
completely. If the error is persistent and still annoys you after this
treatment please send us a bug report (or even better, a fix :-)
Using the PyPy translation tool chain
============================================================
How do I compile PyPy?
----------------------
See the `getting-started`_ guide. Note that at the moment this produces
an executable that contains a lot of things that are hard-coded for your
particular system (including paths and other stuff), so it's not
suitable for being installed or redistributed.
How do I compile my own programs?
---------------------------------
Start from the example of
`pypy/translator/goal/targetnopstandalone.py`_, which you compile by
typing::
python translate_pypy.py targetnopstandalone
You can have a look at intermediate C source code, which is (at the
moment) put in ``/tmp/usession-*/testing_1/testing_1.c``. Of course,
all the function and stuff indirectly used by your ``entry_point()``
function has to be RPython_.
Why isn't there a simpler way of doing that?
--------------------------------------------
One answer is that "officially speaking" supporting this is not a goal
of the PyPy project (RPython is essentially an implementation detail).
A better answer might be that when the target of compilation turns out
not to be RPython, working out *why* can be very difficult, and
working on the annotator to make these messages clearer -- even if
possible -- would take time away from other development tasks.
It's not that writing RPython is difficult, but if there was some kind
of rpythonc compiling tool there would be much more temptation to try
to compile arbitrary, pre-existing Python programs and this is fairly
unlikely to work (to start, there is very little in the way of an
"RPython standard library").
Compiling to other languages
============================================================
Couldn't we simply take a Python syntax tree and turn it into Lisp?
-------------------------------------------------------------------
It's not necessarily nonsense, but it's not really The PyPy Way. It's
pretty hard, without some kind of type inference, to translate, say this
Python::
a + b
into anything significantly more efficient than this Common Lisp::
(py:add a b)
And making type inference possible is what RPython is all about.
You could make ``#'py:add`` a generic function and see if a given CLOS
implementation is fast enough to give a useful speed (but I think the
coercion rules would probably drive you insane first). -- mwh
Speed
============================================================
How fast is PyPy?
-----------------
As of August 2005, PyPy was successfully translated to C. The version
of PyPy that still runs on top of CPython is slower by a factor of 2000
compared to CPython. The first translated version was roughly 300 times
slower than CPython, and current versions (as of the 0.8.0 release) about
10-20 times slower than CPython. On the other hand, the really interesting
question is: Why is PyPy so slow?
.. _whysoslow:
Why is PyPy so slow?
--------------------
Our translation process does not try to optimize the produced code very
much. So far the project has been focused on getting a well tested very
compliant self-contained static Python implementation. During end 2005
and 2006 we are targetting optimizations at various levels. If you then
still think that PyPy is slow then we will have to find a better answer
:-)
.. _`RPython`: coding-guide.html#rpython
.. _`getting-started`: getting-started.html
.. include:: _ref.txt
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