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Generalize the itertools.tee() recipe.

This commit is contained in:
Raymond Hettinger 2009-02-18 20:56:51 +00:00
parent 0654ccd1d2
commit cf984cee93
1 changed files with 21 additions and 21 deletions
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42
Doc/library/itertools.rst
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@ -130,7 +130,7 @@ loops that truncate the stream.
return
indices = list(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
@ -178,7 +178,7 @@ loops that truncate the stream.
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
@ -501,28 +501,28 @@ 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::
Return *n* independent iterators from a single iterable. 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__))
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)
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.
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`.
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`.
.. function:: zip_longest(*iterables[, fillvalue])