From bb94fd829067ad6ba6e2f5a349b962cd272c7e09 Mon Sep 17 00:00:00 2001 From: Raymond Hettinger Date: Wed, 18 Feb 2009 21:04:16 +0000 Subject: [PATCH] Generalize itertools.tee() recipe. --- Doc/library/itertools.rst | 48 +++++++++++++++++++-------------------- 1 file changed, 24 insertions(+), 24 deletions(-) diff --git a/Doc/library/itertools.rst b/Doc/library/itertools.rst index 6e561992e9..a349ef9a16 100644 --- a/Doc/library/itertools.rst +++ b/Doc/library/itertools.rst @@ -112,7 +112,7 @@ loops that truncate the stream. return indices = range(r) yield tuple(pool[i] for i in indices) - while 1: + while True: for i in reversed(range(r)): if indices[i] != i + n - r: break @@ -521,28 +521,28 @@ loops that truncate the stream. .. function:: tee(iterable[, n=2]) - Return *n* independent iterators from a single iterable. The case where ``n==2`` - is equivalent to:: - - def tee(iterable): - def gen(next, data={}): - for i in count(): - if i in data: - yield data.pop(i) - else: - data[i] = next() - yield data[i] - it = iter(iterable) - return gen(it.next), gen(it.next) - - Note, once :func:`tee` has made a split, the original *iterable* should not be - used anywhere else; otherwise, the *iterable* could get advanced without the tee - objects being informed. - - Note, this member of the toolkit may require significant auxiliary storage - (depending on how much temporary data needs to be stored). In general, if one - iterator is going to use most or all of the data before the other iterator, it - is faster to use :func:`list` instead of :func:`tee`. + Return *n* independent iterators from a single iterable. Equivalent to:: + + def tee(iterable, n=2): + it = iter(iterable) + deques = [collections.deque() for i in range(n)] + def gen(mydeque): + while True: + if not mydeque: # when the local deque is empty + newval = next(it) # fetch a new value and + for d in deques: # load it to all the deques + d.append(newval) + yield mydeque.popleft() + return tuple(gen(d) for d in deques) + + Once :func:`tee` has made a split, the original *iterable* should not be + used anywhere else; otherwise, the *iterable* could get advanced without + the tee objects being informed. + + This itertool may require significant auxiliary storage (depending on how + much temporary data needs to be stored). In general, if one iterator uses + most or all of the data before another iterator starts, it is faster to use + :func:`list` instead of :func:`tee`. .. versionadded:: 2.4 @@ -690,7 +690,7 @@ which incur interpreter overhead. return indices = [0] * r yield tuple(pool[i] for i in indices) - while 1: + while True: for i in reversed(range(r)): if indices[i] != n - 1: break -- 2.49.0