[docs] [issue16774] Additional recipes for itertools docs

[Alexey Kachayev]

Alexey Kachayev added the comment:

It's hard to evaluate how popular given recipes, but:
* drop is opposite to take, so it's as popular as take
* the same situation with splitat, splitby - it's one case of partition that's hard to write each time with enumerator (partition is already in documentation)
* takelast, droplast was added cause itertools.islice doesn't support negative indices (which is ok). both functions have not obvious implementation - I'm sure that recipes will be good example for users how to work with iterators even if concrete functions aren't so widely-spreaded

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue16774>
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