[Python-Dev] Proposal for a new itertools function: iwindow

[Nick Coghlan]

Raymond Hettinger wrote:
> No thanks.  The resolution of this one was that windowing iterables is 
> not a good idea.  It is the natural province of sequences, not 
> iterables.  With sequences, it is a matter of using an index and 
> offset.  With iterables, there is a great deal of data shifting.  Also 
> note that some of the uses are subsumed by collections.deque().

Interesting - the old 'hammer-nail' tunnel vision strikes again, I guess.

So moving the question to a different part of the docs, would it make sense to 
include a deque recipe showing how to use a deque in a generator to permit 
windowing of an arbitrary iterator? Something like:

def window(iterable, window_len=2, window_step=1):
      itr = iter(iterable)
      step_range = xrange(window_step)
      current_window = collections.deque(islice(itr, window_len))
      while window_len == len(current_window):
          yield current_window
          for idx in step_range:
              current_window.popleft()
          current_window.extend(islice(itr, window_step))

Even if an application doesn't use the generator approach directly, it still 
illustrates how to use a deque for windowing instead of as a FIFO queue or a 
stack.

> The thought process was documented in a series of newsgroup postings:
>    http://groups.google.com/group/comp.lang.python/msg/026da8f9eec4becf

Thanks for that reference - I was searching the wrong list, so I didn't find it.

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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