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Tue Jul 13 17:33:42 CEST 2004 · https://mail.python.org/pipermail/python-dev/2004-July/046122.html

[Jim Fulton]
> I still don't like it, because it hides the return.
> 
> I'd rather do:
> 
>        if (self->foo != NULL && (vret = visit(self->foo, arg)))
>                return vret;
> 
> than
> 
>         VISIT(self->foo)

I don't believe you <0.5 wink>.  Here, rewrite this:

	VISIT(self->readline);
	VISIT(self->read);
	VISIT(self->file);
	VISIT(self->memo);
	VISIT(self->stack);
	VISIT(self->pers_func);
	VISIT(self->arg);
	VISIT(self->last_string);
	VISIT(self->find_class);
                return 0;

That's the current Unpickler_traverse, and it's utterly typical.  In
context, hiding the return doesn't matter:  no computation is done
between VISIT invocations.

> So I'm not interested in the macro myself. :)

That's fair, but the lack of one will make correct docs for
tp_traverse functions clumsier to write and read (you'll have to write
out the tedious & error-prone (*because* tedious) expansion instead --
and that will encourage readers to code their tp_traverses in this
brittle way too).

> I'll say again that I don't like calling the return from the visit
> proc an error indicator, because it's not,

I agree (again <wink>).

> and because it goes against the common idiom of using a negative return to
> indicate an error.

Well, it's not an error indicator (although it *may* be), so error
idioms don't apply.  I'll change that bit of the docs.

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C API Macro to decref and set to NULL)