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Document when to use izip_longest().

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Raymond Hettinger 2008-01-22 19:51:41 +00:00
parent 74b8e76ec1
commit 48c6293500
1 changed files with 6 additions and 15 deletions
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21
Doc/library/itertools.rst
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@ -269,22 +269,13 @@ loops that truncate the stream.
When no iterables are specified, returns a zero length iterator instead of
raising a :exc:`TypeError` exception.
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
``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 ``izip(*[chain(s,
[None]*(n-1))]*n)``.
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 ``izip(*[iter(s)]*n)``.
Note, when :func:`izip` is used with unequal length inputs, subsequent
iteration over the longer iterables cannot reliably be continued after
:func:`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 ``it.next()``). In general, :func:`izip`
should only be used with unequal length inputs when you don't care about
trailing, unmatched values from the longer iterables.
:func:`izip` should only be used with unequal length inputs when you don't
care about trailing, unmatched values from the longer iterables. If those
values are important, use :func:`izip_longest` instead.
.. function:: izip_longest(*iterables[, fillvalue])