[Python-Dev] ctypes: is it intentional that id() is the only way to get the address of an object?
On Fri, 18 Jan 2019 03:00:54 +0000
MRAB <python at mrabarnett.plus.com> wrote:
> On 2019-01-18 00:48, Gregory P. Smith wrote:
> > I've heard that libraries using ctypes, cffi, or cython code of various
> > sorts in the real world wild today does abuse the unfortunate side
> > effect of CPython's implementation of id(). I don't have specific
> > instances of this in mind but trust what I've heard: that it is happening.
> > id() should never be considered to be the PyObject*.? In as much as code
> > shouldn't assume it is running on top of a specific CPython implementation.
> > If there is a _need_ to get a pointer to a C struct handle referencing a
> > CPython C API PyObject, we should make an explicit API for that rather
> > than the id() hack.? That way code can be explicit about its need, and
> > code that is just doing a funky form of identity tracking without using
> > is and is not can continue using id() without triggering regressive
> > behavior on VMs that don't have a CPython compatible PyObject under the
> > hood by default.
> > [who uses id() anyways?]
> I use it in some of my code.
> If I want to cache some objects, I put them in a dict, using the id as
> the key. If I wanted to locate an object in a cache and didn't have
> id(), I'd have to do a linear search for it.
Indeed. I've used it for the same purpose in the past (identity-dict).