[Python-Dev] Highlighting reference-stealing APIs [was Re: cpython: Fix email post-commit review comments.] (original) (raw)

David Malcolm dmalcolm at redhat.com
Thu Apr 19 02:01:30 CEST 2012

On Thu, 2012-04-19 at 10:48 +1200, Greg Ewing wrote:

Antoine Pitrou wrote:

> (and here we see why reference-stealing APIs are a nuisance: because > you never know in advance whether a function will steal a reference or > not, and you have to read the docs for each and every C API call you > make) Fortunately, they're very rare, so you don't encounter them often. Unfortunately, they're very rare, so you're all the more likely to forget about them and get bitten. Functions with ref-stealing APIs really ought to have a naming convention that makes them stand out and remind you to consult the documentation. FWIW my refcount static analyzer adds various new compile-time attributes to gcc: http://gcc-python-plugin.readthedocs.org/en/latest/cpychecker.html#marking-functions-that-steal-references-to-their-arguments so you can write declarations like these:

extern void bar(int i, PyObject *obj, int j, PyObject *other) CPYCHECKER_STEALS_REFERENCE_TO_ARG(2) CPYCHECKER_STEALS_REFERENCE_TO_ARG(4);

There's a similar attribute for functions that return borrowed references:

PyObject *foo(void) CPYCHECKER_RETURNS_BORROWED_REF;

Perhaps we should add such attributes to the headers for Python 3.3? (perhaps with a different naming convention?)

Hope this is helpful Dave

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