"Martin v. Löwis", 21.03.2011 23:44:
Am 21.03.2011 11:58, schrieb Stefan Behnel:
Guido van Rossum, 21.03.2011 03:46:
Thanks for the clarifications. I now have a much better understanding
of what Cython is. But I'm not sold. For one, your attitude about
strict language compatibility worries me when it comes to the stdlib.
Not sure what you mean exactly. Given our large user base, we do worry a
lot about things like backwards compatibility, for example.
If you are referring to compatibility with Python, I don't think anyone
in the project really targets Cython as a a drop-in replacement for a
Python runtime. We aim to compile Python code, yes, and there's a
hand-wavy idea in the back of our head that we may want a plain Python
compatibility mode at some point that will disable several important
optimisations.
I think that's the attitude Guido worries about: if you don't have the
desire to provide 100% Python compatibility under all circumstances
(i.e. including if someone passes parameters of "incorrect" types),
then there is very little chance that we would replace a Python module
with a Cython-compiled one.
We are aware of potential differences and generally consider (most of) them
bugs. We even try to keep our exception messages in line with CPython
(usually py3k, CPython has changed its own messages quite a bit during its
lifetime, as our doctests can tell), and try to make optimised code as safe
as possible by default. For example, we automatically raise TypeErrors on
invalid arguments *iff* there is a user declared type for them, and we
raise OverflowErrors during C type conversions and even some C calculations
unless explicitly disabled by the user. If in doubt, we always try to copy
CPython's own behaviour.
So it's almost always up to the user to explicitly divert from normal
Python behaviour for performance reasons. And Cython's type driven code
adaptations allow for a *very* broad range of explicit diversions that
users can deploy in order to balance the user visible impact with the
performance requirements.
Stefan
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