On Fri, 18 Jan 2019 at 09:52, Steven D'Aprano <st...@pearwood.info> wrote: > Code-wise, I'm not doing anything with ctypes. > > Language-wise, I'm trying to get a definitive answer of whether or not > id() returning the address of the object should be a guaranteed feature > or not. > > Across the entire Python ecosystem, no it isn't, as Jython and > IronPython return consecutive integers. But should we consider it an > intentional part of the CPython API? > > There are developers who insist that when it comes to CPython, id() > returning the object address is an intentional feature that they can and > do rely on, because (so I was told by one of them) that using id() is > the only way to get the address of an object from pure-Python. > > According to this claim, using id() to get the address for use in ctypes > is the correct and only way to do it, and this is a deliberate design > choice by the core devs rather than an accident of the implementation. > So long as you know you are using CPython, this is (so I was told) > completely safe. > > In the grand scheme of things this may be a pretty minor issue. But I > suspect that it could be a pain point for implementations like PyPy that > support both objects that move and a ctypes emulation.
As per Eryk Sun's reply, the "correct" way to get an object address is by using ctypes.py_object. Supporting py_object may be a pain point for other implementations that emulate ctypes, but then again, so is supporting the whole CPython C API (which is where the py_object type is needed, so it's basically the same problem). So to answer your question, I'd say that no, id() returning the object address is not, and should not be, a guaranteed aspect of CPython, and the motivating issue of ctypes is solved within ctypes itself by using py_object. Paul _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
