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author | Thomas Wouters <thomas@python.org> | 2006-04-21 10:40:58 (GMT) |
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committer | Thomas Wouters <thomas@python.org> | 2006-04-21 10:40:58 (GMT) |
commit | 49fd7fa4431da299196d74087df4a04f99f9c46f (patch) | |
tree | 35ace5fe78d3d52c7a9ab356ab9f6dbf8d4b71f4 /Doc/lib/libitertools.tex | |
parent | 9ada3d6e29d5165dadacbe6be07bcd35cfbef59d (diff) | |
download | cpython-49fd7fa4431da299196d74087df4a04f99f9c46f.zip cpython-49fd7fa4431da299196d74087df4a04f99f9c46f.tar.gz cpython-49fd7fa4431da299196d74087df4a04f99f9c46f.tar.bz2 |
Merge p3yk branch with the trunk up to revision 45595. This breaks a fair
number of tests, all because of the codecs/_multibytecodecs issue described
here (it's not a Py3K issue, just something Py3K discovers):
http://mail.python.org/pipermail/python-dev/2006-April/064051.html
Hye-Shik Chang promised to look for a fix, so no need to fix it here. The
tests that are expected to break are:
test_codecencodings_cn
test_codecencodings_hk
test_codecencodings_jp
test_codecencodings_kr
test_codecencodings_tw
test_codecs
test_multibytecodec
This merge fixes an actual test failure (test_weakref) in this branch,
though, so I believe merging is the right thing to do anyway.
Diffstat (limited to 'Doc/lib/libitertools.tex')
-rw-r--r-- | Doc/lib/libitertools.tex | 27 |
1 files changed, 25 insertions, 2 deletions
diff --git a/Doc/lib/libitertools.tex b/Doc/lib/libitertools.tex index 421d647..20bbc8d 100644 --- a/Doc/lib/libitertools.tex +++ b/Doc/lib/libitertools.tex @@ -276,12 +276,30 @@ by functions or loops that truncate the stream. def izip(*iterables): iterables = map(iter, iterables) while iterables: - result = [i.next() for i in iterables] + result = [it.next() for it in iterables] yield tuple(result) \end{verbatim} \versionchanged[When no iterables are specified, returns a zero length - iterator instead of raising a TypeError exception]{2.4} + iterator instead of raising a \exception{TypeError} + exception]{2.4} + + Note, the left-to-right evaluation order of the iterables is guaranteed. + This makes possible an idiom for clustering a data series into n-length + groups using \samp{izip(*[iter(s)]*n)}. For data that doesn't fit + n-length groups exactly, the last tuple can be pre-padded with fill + values using \samp{izip(*[chain(s, [None]*(n-1))]*n)}. + + Note, when \function{izip()} is used with unequal length inputs, subsequent + iteration over the longer iterables cannot reliably be continued after + \function{izip()} terminates. Potentially, up to one entry will be missing + from each of the left-over iterables. This occurs because a value is fetched + from each iterator in-turn, but the process ends when one of the iterators + terminates. This leaves the last fetched values in limbo (they cannot be + returned in a final, incomplete tuple and they are cannot be pushed back + into the iterator for retrieval with \code{it.next()}). In general, + \function{izip()} should only be used with unequal length inputs when you + don't care about trailing, unmatched values from the longer iterables. \end{funcdesc} \begin{funcdesc}{repeat}{object\optional{, times}} @@ -517,4 +535,9 @@ def pairwise(iterable): pass return izip(a, b) +def grouper(n, iterable, padvalue=None): + "grouper(3, 'abcdefg', 'x') --> ('a','b','c'), ('d','e','f'), ('g','x','x')" + return izip(*[chain(iterable, repeat(padvalue, n-1))]*n) + + \end{verbatim} |