Feature Requests item #1757395, was opened at 2007-07-20 04:12
Message generated for change (Comment added) made by rhettinger
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Category: Python Library
Group: Python 2.6
Status: Closed
Resolution: Rejected
Priority: 5
Private: No
Submitted By: Alexander Dutton (asdutton)
Assigned to: Nobody/Anonymous (nobody)
Summary: splice() function for itertools
Initial Comment:
Could we have a splice function in itertools? I see there was once a roundrobin
proposal (#756253), but it was three years ago ...
Here's an alternate implementation:
def splice(*args):
"""splice(*iterables) --> iterator
Returns an iterator whose next() method returns an element from each of the
iterables in turn before starting again with the first iterable."""
iters = list(args)
n = len(iters)
i = 0
while n>0:
i %= n
try:
yield iters[i].next()
i += 1
except StopIteration, e:
n -= 1
iters[i:i+1] = []
raise StopIteration
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>Comment By: Raymond Hettinger (rhettinger)
Date: 2007-07-22 11:51
Message:
Logged In: YES
user_id=80475
Originator: NO
FWIW, here is the optimized recipe:
def roundrobin(*iterables):
pending = deque(iter(i).next for i in reversed(iterables))
rotate, pop, _StopIteration = pending.rotate, pending.pop,
StopIteration
while pending:
try:
while 1:
yield pending[-1]()
rotate()
except _StopIteration:
pop()
----------------------------------------------------------------------
Comment By: Raymond Hettinger (rhettinger)
Date: 2007-07-22 11:19
Message:
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user_id=80475
Originator: NO
The reasons for rejecting the roundrobin proposal still apply three years
later. It is somewhat use case challenged.
FWIW, there is a reasonably efficient pure python implementation using
collections.deque(). See http://docs.python.org/lib/deque-recipes.html for
an unoptimized recipe which can be fine-tuned to use bound methods and all
local variables for better speed.
----------------------------------------------------------------------
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