[Python-Dev] Let's update CObject API so it is safe and regular! (original) (raw)

Brett Cannon brett at python.org
Wed Apr 1 17:21:48 CEST 2009

On Tue, Mar 31, 2009 at 20:34, Guido van Rossum <guido at python.org> wrote:

Can you get Jim Fulton's feedback? ISTR he originated this.

I thought Neal started this idea?

-Brett

On Tue, Mar 31, 2009 at 12:14 PM, Larry Hastings <larry at hastings.org> wrote: > > The CObject API has two flaws. > > First, there is no usable type safety mechanism. You can store a void > *object, and a void *description. There is no established schema for > the description; it could be an integer cast to a pointer, or it could > point to memory of any configuration, or it could be NULL. Thus users > of the CObject API generally ignore it--thus working without any type > safety whatsoever. A programmer could crash the interpreter from pure > Python by mixing and matching CObjects from different modules (e.g. give > "curses" a CObject from "ctypes"). > > Second, the destructor callback is defined as taking either one or > two parameters, depending on whether the "descr" pointer is non-NULL. One > can debate the finer points of what is and isn't defined behavior in > C, but at its heart this is a sloppy API. > > MvL and I discussed this last night and decided to float a revision of > the API. I wrote the patch, though, so don't blame Martin if you don't > like my specific approach. > > The color of this particular bike shed is: > * The PyCObject is now a private data structure; you must use accessors. > I added accessors for all the members. > * The constructors and the main accessor (PyCObjectAsVoidPtr) now all > require a "const char *type" parameter, which must be a non-NULL C > string of non-zero length. If you call that accessor and the "type" > is invalid or doesn't match, it fails. > * The destructor now takes the PyObject *, not the PyCObject *. You > must use accessors to get your hands on the data inside to free it. > > Yes, you can easily skip around the "matching type" restriction by > calling PyCObjectAsVoidPtr(cobj, PyCObjectGetType(cobj)). The point > of my API changes is to encourage correct use. > > I've posted a patch implementing this change in the 3.1 trunk to the > bug tracker: > > http://bugs.python.org/issue5630 > > I look forward to your comments! > > > /larry/ > _> ________________________ > Python-Dev mailing list > Python-Dev at python.org > http://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: > http://mail.python.org/mailman/options/python-dev/guido%40python.org >

-- --Guido van Rossum (home page: http://www.python.org/~guido/<http://www.python.org/%7Eguido/> )

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