[Python-Dev] cffi in stdlib

Ronald Oussoren ronaldoussoren at mac.com
Wed Feb 27 08:29:47 CET 2013

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. 

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)

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.

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?

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' has ctype 'struct $CGFloat' 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".


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