Re: possible bug in Pyrex

On Feb 25, 2010, at 3:29 PM, Greg Ewing wrote:

> Stefan Behnel wrote:
>
>> As a general rule of thumb, the code generated by Cython is quite a  =

>> bit
>> longer and substantially faster than the corresponding Pyrex code.
>
> Be careful you're not comparing apples with oranges here,
> though. Pyrex is capable of generating quite efficient code
> for many things, it's just not as automatic as Cython.

Yes, for example, both can generate near optimal code with heavy use  =

of the Python/C API. One of Cython's goals is that users no need to  =

know this API to generate optimal code (or at least as close as we can  =

get). There are other things, such as argument unpacking, that can't  =

be as easily controlled by the user.

> For example, I gather that Cython will generate a test
> for a list object and index it using list-specific calls
> in that case.
>
> Recent versions of Pyrex will also use list-specific calls,
> but only if you declare it as a list. Theoretically this
> should be even faster, because there is no run-time test
> involved.


If an object is declared as a list, no run-time test will be generated  =

in Cython either. There is a slight performance penalty for, say,  =

indexing into a non-list with a cdef int, but it is relatively small  =

and yields large gains for the common case of indexing into a list.

- Robert