New submission from Larry Hastings: CPython API "functions" implemented as macros can expand into either rvalues or statements. Most expand into statements (often using the do {} while (0) syntactic sugar trick), but occasionally they're legal as rvalues. As of this writing Py_INCREF works as an rvalue. But discussion on another tracker issue (#17206) proposes changing the implementation in such a way that it will only be usable as a statement. Although it's mildly unlikely, it's certainly possible that this will break somebody's code. I propose that the documentation make an explicit ruling on whether macros are usable as rvalues or as statements. Perhaps a blanket statement would suffice, "all macros are only supported for use as statements except where explicitly noted", then annotate specific macros that are supported for use as rvalues. Though that raises the question of acknowledging in the documentation that some things are macros--I think the documentation glosses over that fact right now. Note: I added you three (Georg, Mark, Martin) as I thought you might have an opinion on this one way or the other. If you're not interested, my apologies. ---------- assignee: docs@python components: Documentation messages: 185646 nosy: Mark.Shannon, docs@python, georg.brandl, larry, loewis priority: normal severity: normal stage: needs patch status: open title: Make documentation about macros in C API explicit about rvalue vs statement type: enhancement versions: Python 3.4 _______________________________________ Python tracker http://bugs.python.org/issue17589 _______________________________________