[Python-Dev] Negative times behaviour in itertools.repeat for Python maintenance releases (2.7, 3.3 and maybe 3.4)

[Larry Hastings]

On 01/27/2014 06:00 PM, Vajrasky Kok wrote:
> On Mon, Jan 27, 2014 at 9:13 PM, Larry Hastings <larry at hastings.org> wrote:
>> I apologize for not making myself clear.  But that's part of what I meant,
>> yes: we should preserve the existing behavior of times=-1 when passed in by
>> position or by keyword.  However, we should *also* add a deprecation warning
>> when passing times=-1 by keyword, suggesting that they use times=None
>> instead.  The idea is that we could eventually remove the PyTuple_Size check
>> and make times=-1 always behave like times=0.  In practice it'd be okay with
>> me if we never did, or at least not until Python 4.
>>
> So we only add deprecation warning to only times=-1 via keyword or for
> all negative numbers to times via keyword?
>
> I mean, what about:
>>>> from itertools import repeat
>>>> list(repeat('a', times=-2))
>

I should have been even *more* precise!  When I said "times=-1" I really 
meant all negative numbers.  (I was trying to abbreviate it as -1, as my 
text was already too long and unwieldly.)

I propose the logic be equivalent to this, handwaving for clarity 
boilerplate error handling (the real implementation would handle 
PyArg_ParseParseTupleAndKeywords or PyLong_ToPy_ssize_t failing):

    PyObject *element, times = Py_None;
    Py_ssize_t cnt;
    PyArg_ParseTupleAndKeywords(args, kwargs, "O|O:repeat", kwargs,
    &element, &times);
    if times == Py_None
        cnt = -1
    else
         cnt = PyLong_ToPy_ssize_t(times)
         if cnt < 0
             if "times" was passed by keyword
                 issue DeprecationWarning, "use repeat(o, times=None) to
    repeat indefinitely"
             else
                 cnt = 0

(For those of you who aren't familiar with the source: "cnt" is the 
internal variable used to set the repeat count of the iterator.  If 
"cnt" is < 0, the iterator repeats forever.)

If in the future we actually removed the deprecated behavior, the last 
"if" block would change simply to

         if cnt < 0
             cnt = 0



//arry/
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