[Patches] [ python-Patches-1749857 ] itertools.getitem()

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Patches item #1749857, was opened at 2007-07-08 04:33
Message generated for change (Comment added) made by rhettinger
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Category: Modules
Group: Python 2.6
>Status: Closed
>Resolution: Rejected
Priority: 5
Private: No
Submitted By: Walter Dörwald (doerwalter)
Assigned to: Raymond Hettinger (rhettinger)
Summary: itertools.getitem()

Initial Comment:
This patch adds itertools.getitem() which is basically equivalent to the following python code:

_default = object()

def getitem(iterable, index, default=_default):
   try:
      return list(iterable)[index]
   except IndexError:
      if default is _default:
         raise
      return default

but without materializing the complete list. Negative indexes are supported too.

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>Comment By: Raymond Hettinger (rhettinger)
Date: 2007-07-31 02:03

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Originator: NO

Rejected after an offline discussion with the OP.

The use case for getitem(n) with n as a negative number depended on an
unlikely combination of circumstances:

* you have an iterable that is not a sequence (otherwise, just use
s[-n]).
* the iterable is somewhat large (otherwise, just list it into memory)
* the iterable is finite (otherwise, getitem() dies in a infinite loop)
* you only want one entry (otherwise, you'll have make multiple passes)
* that entry is located near the end (otherwise getitem() is memory
intensive)
* you know the entry's offset from the end but not from the beginning
* identifying the record of interest depends only on its position, not its
content

In the common case where the index is zero, the preferred spelling is to
use the next() method -- that is its purpose.  For cases where the index is
a positive integer, uing islice(it, n).next() suffices though it doesn't
have the cute feature for a default value.



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