[Python-Dev] Negative times behaviour in itertools.repeat for Python maintenance releases (2.7, 3.3 and maybe 3.4)
Larry Hastings
larry at hastings.org
Tue Jan 28 03:24:25 CET 2014
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, ×);
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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