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

Vajrasky Kok sky.kok at speaklikeaking.com
Tue Jan 28 03:26:17 CET 2014

On Mon, Jan 27, 2014 at 9:13 PM, Larry Hastings <larry at hastings.org> wrote:

While it's a bug, it's a very minor bug. As Python 3.4 release manager, my position is: Python 3.4 is in beta, so let's not change semantics for purity's sakes now. I'm -0.5 on adding times=None right now, and until we do we can't deprecate the old behavior.

I bow to your decision, Larry. So I believe the doc fix is required then. I propose these for doc fix:

  1. Keeps the status quo

repeat.doc 'repeat(object [,times]) -> create an iterator which returns the object\nfor the specified number of times. If not specified, returns the object\nendlessly.'

We don't explain the meaning of negative times. Well, people shouldn't repeat with negative times because statement such as, "Kids, repeat the push-up negative two times more.", does not make sense.

  1. Explains the negative times, ignores the keyword

repeat.doc 'repeat(object [,times]) -> create an iterator which returns the object\nfor the specified number of times. If not specified, returns the object\nendlessly. Negative times means zero repetitions.'

The signature repeat(object [,times]) suggest this function does not accept keyword as some core developers have stated. So if the user uses keyword with this function, well, it's too bad for them.

  1. Explains the negative times, warns about keyword

repeat.doc 'repeat(object [,times]) -> create an iterator which returns the object\nfor the specified number of times. If not specified, returns the object\nendlessly. Negative times means zero repetitions. This function accepts keyword argument but the behaviour is buggy and should be avoided.'

  1. Explains everything

repeat.doc 'repeat(object [,times]) -> create an iterator which returns the object\nfor the specified number of times. If not specified, returns the object\nendlessly. Negative times means zero repetitions via positional-only arguments. -1 value for times via keyword means endless repetitions and is same as omitting times argument and other negative number for times means endless repetitions as well but with different implementation.'

If you are wondering about the last statement:

from itertools import repeat list(repeat('a', times=-4)) Traceback (most recent call last): File "", line 1, in OverflowError: Python int too large to convert to C ssize_t a = repeat('a', times=-4) next(a) 'a' next(a) 'a' a = repeat('a', times=-1) next(a) 'a' next(a) 'a' list(repeat('a', times=-1)) ... freezes your computer ...

Which one is better? Once we settle this, I can think about the doc fix for Doc/library/itertools.rst.

Vajrasky

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