[Python-Dev] ctypes: is it intentional that id() is the only way to get the address of an object?
python at mrabarnett.plus.com
Thu Jan 17 22:00:54 EST 2019
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.
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