[Python-Dev] cffi in stdlib (original) (raw)

Maciej Fijalkowski fijall at gmail.com
Wed Feb 27 10:06:07 CET 2013

On Wed, Feb 27, 2013 at 9:29 AM, Ronald Oussoren <ronaldoussoren at mac.com> wrote:

On 26 Feb, 2013, at 16:13, Maciej Fijalkowski <fijall at gmail.com> wrote:

Hello.

I would like to discuss on the language summit a potential inclusion of cffi[1] into stdlib. The API in general looks nice, but I do have some concens w.r.t. including cffi in the stdlib. 1. Why is cffi completely separate from ctypes, instead of layered on top of it? That is, add a utility module to ctypes that can parse C declarations and generate the right ctypes definitions.

Because ctypes API is a mess and magic. We needed a cleaner (and much smaller) model.

2. Cffi has a dependencies on pycparser and that module and its dependencies would therefore also be added to the stdlib (even if they'd be hidden in the cffi package)

Yes. pycparser and ply.

3. Cffi basicly contains a (limited) C parser, and those are notoriously hard to get exactly right. Luckily cffi only needs to interpret declarations and not the full language, but even so this can be a risk of subtle bugs.

It seems to work.

4. And finally a technical concern: how well does cffi work with fat binaries on OSX? In particular, will the distutils support generate cached data for all architectures supported by a fat binary?

no idea.

Also, after playing around with it for 5 minutes I don't quite understand how to use it. Let's say I want to wrap a function "CGPoint CGPointMake(CGFloat x, CGFloat y)". Is is possible to avoid mentioning the exact typedef for CGFloat somewhere? I tried using: ffi.cdef("typedef ... CGFloat; typedef struct { CGFloat x; CGFloat y; } CGPoint; CGPoint CGPointMake(CGFloat x, CGFloat y);") But that results in an error when calling verify: TypeError: field 'struct CGPoint.x′hasctype′structCGPoint.x' has ctype 'struct CGPoint.x′hasctype′structCGFloat' of unknown size From a first glance this doesn't seem to buy me that much w.r.t. ctypes, I still have to declare the actual type of CGFloat which is documented as "some floating point type". Ronald

typedef ... is assumed to be a struct. Copy pasting from documentation, we might want to have a better support for that, but what you do right now is to do:

ffi.cdef("const int mysize;") lib = ffi.verify("const int mysize = sizeof(THE_TYPE);") print lib.mysize

which will tell you the size (and then you can pick up which float you want). I agree that some generic support for that would be cool.

Cheers, fijal

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