[Python-ideas] Queue suggestions

[Gregory P. Smith]

Do you have a compelling use case for Queue.rotate?

On Thu, May 22, 2008 at 10:23 PM, George Sakkis <george.sakkis at gmail.com> wrote:
> I'd like to propose a signature simplification and a new method for
> the Queue.Queue class:
>
> 1) Drop the optional `block` argument from put() and get(), since all
> the meaningful combinations of  (block, timeout) are equivalent to
> passing block = (timeout is None or timeout>0). IOW, instead of
> passing block=False pass timeout=0 (or negative). Obviously this is to
> be considered for 3.x only.
>
> 2) Add a new `rotate` method as the atomic equivalent of
> put_nowait(get_nowait()). Currently I use the following subclass but
> it would be nice to have it in the base Queue:
>
> class RQueue(Queue):
>
>    def rotate(self, n=1):
>        '''Rotate this queue n steps to the left (if it is not empty).
>
>        Rotating one step is equivalent to an atomic
> q.put_nowait(q.get_nowait()).
>        '''
>        if n < 0:
>            raise ValueError('n must be non-negative')
>        self.mutex.acquire()
>        try:
>            if not self._empty():
>                self._rotate(n)
>        finally:
>            self.mutex.release()
>
>    def __init__(self, maxsize=0):
>        Queue.__init__(self, maxsize)
>        if hasattr(self.queue, 'rotate'):  # deque has rotate() since v2.5
>            def _rotate(n):
>                # negative n for left rotate
>                self.queue.rotate(-n)
>        else:
>            def _rotate(n):
>                put,get = self._put, self._get
>                for i in xrange(n):
>                    put(get())
>        self._rotate = _rotate
>
>
> What do you think ?
>
> George
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