[issue14705] Add 'bool' format character to PyArg_ParseTuple*

[Larry Hastings]

Larry Hastings <larry at hastings.org> added the comment:

Attached is rev 3 of my patch, incorporating mainly backing out of dumb ideas.  Thanks for the feedback, Serhiy and Mark!


> My name is Serhiy. :)

My genuine apologies!  In my defense it was rather late.


> 'P' has the advantage that you can safely backward-compatibly
> remove the restriction by replacing 'P' on 'p'. :)

That's not a reason to use 'P'.  Why you should use 'P' in the first place?


> In this line in the patch (Python/getargs.c):
> +        if (val == -1 || PyErr_Occurred()) {
> Isn't that call to PyErr_Occurred() redundant?

Certainly one of the two expressions is!

My thinking was: if the call fails, then the val == -1 will be an early-exit and we can save the call to PyErr_Occurred.  This was always a dumb idea, as the 99.999999% case is that PyObject_IsTrue succeeds, in which case we would have called PyErr_Occured anyway.  Some savings!

I can't find any documentation on permitted return values from nb_bool.  However, PyObject_IsTrue itself says about its own return value:

    /* if it is negative, it should be either -1 or -2 */

So I definitely shouldn't check specifically for -1.

Having meditated on it, I think either I should either just call PyErr_Occured, check for explicit failure (val < 0), or explicit success (val >= 0).  I've opted for the last of those.


I considered briefly trying to make 'P' handle subclasses of bool.  But then I hit the problem of: okay, what now?  Call nb_bool?  I note that bool itself doesn't define nb_bool.  Anyway, what lunatic would subclass bool?


I'm really on the fence about 'P'.  Serhiy is definitely pro-, everyone else seems to think it shouldn't be used.  However nobody has argued against its inclusion.  At the moment I'm -0 on it myself, but since the code is written...

Do we have an anti-champion?

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Added file: http://bugs.python.org/file25465/larry.parse.tuple.p.and.P.3.diff

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