[Python-Dev] ctypes: is it intentional that id() is the only way to get the address of an object?

MRAB 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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