itertools roundrobin()

[jackdied]

BPO	756253
Nosy	@rhettinger, @jackdied
Files	itertoolsmodule.c.diff: Modules/itertoolsmodule.c context diff against cvs test_itertools.py.diff: Lib/test/test_itertools.py patch itertoolsmodule.c: cleaned up patch libitertools.text.diff: documentation path test_itertools.py: updated test patch

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/rhettinger'
closed_at = <Date 2004-04-30.22:58:02.000>
created_at = <Date 2003-06-17.21:35:14.000>
labels = ['extension-modules']
title = 'itertools roundrobin()'
updated_at = <Date 2004-04-30.22:58:02.000>
user = 'https://github.com/jackdied'

bugs.python.org fields:

activity = <Date 2004-04-30.22:58:02.000>
actor = 'rhettinger'
assignee = 'rhettinger'
closed = True
closed_date = None
closer = None
components = ['Extension Modules']
creation = <Date 2003-06-17.21:35:14.000>
creator = 'jackdied'
dependencies = []
files = ['5391', '5392', '5393', '5394', '5395']
hgrepos = []
issue_num = 756253
keywords = ['patch']
message_count = 9.0
messages = ['44061', '44062', '44063', '44064', '44065', '44066', '44067', '44068', '44069']
nosy_count = 2.0
nosy_names = ['rhettinger', 'jackdied']
pr_nums = []
priority = 'normal'
resolution = 'rejected'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue756253'
versions = ['Python 2.4']

[jackdied]

a patch to add the roundrobin() and window() objects to
the itertools module. Hettinger has already seen the
implementation of roundrobin, but not window.

test_itertools.py in a seperate patch

[rhettinger]

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*Please post the tests to this patch and close the other patch.

*Add a documentation patch to this patch

*Let's drop the addition of window(). The C code for it is less
than beautiful and offers only a minimal performance gain
over the pure python equivalent. I've added the pure python
version to the docs so folks can cut and paste it if they need
it. Sorry for the wild goose chase (I had expected the C
version to be much cleaner and faster and that the python
verions would've been harder -- actual code was needed for
me to see it).

• In roundrobin_next(), replace the % operator with:
  if (lz->iternum==lz->itersize) lz-iternum=0;

• In roundrobin_next(), remove the extra blank line
  following "long listsize;"

• Fixup the indentation, currently it is a mix of spaces and
  tabs. It should be just pure tabs.

• Replace the variable name 'lz' with 'rr'. I should have
  changed that in other places too but for new code it
  should be fixed.

• 'unti' is mispelled in the docstring.

[jackdied]

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added Lib/test/test_itertools.py patch here, deleted old
item that just had that patch in it

[jackdied]

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pushed to 2.4
I'll put up patches that incorporate rhettinger's feedback
soon, and definitely in time for the 2.4 branch.

[rhettinger]

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Great. I look forward to it.

[rhettinger]

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Jack, are you still working on this one?

[jackdied]

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The newest triplet of module/test/documentation incorporate
your change suggestions. That includes the removal of the
window() stuff, so these only contain roundrobin() related
patches.

[rhettinger]

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Decided not to include this in Py2.4.

The tool is not sufficiently general. It has only one use
case and arguably that case is better served with
collections.deque().

The point in favor of the tool is that it cannot be
constructed from other itertools.

[rhettinger]

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For the record, here a simple and efficient roundrobin task
server based on collections.deque:

def roundrobin(*iterables):
    pending = deque(iter(i).next for i in iterables)
    gettask, scheduletask = pending.popleft, pending.append
    while pending:
        task = gettask()
        try:
            yield task()
        except StopIteration:
            continue
        scheduletask(task)

for value in roundrobin('abc', 'd', 'efgh'):
    print value