[issue31108] add __contains__ for list_iterator (and others) for better performance

[Terry J. Reedy]

Terry J. Reedy added the comment:

Sorry, I mistakenly assumed, without carefully checking the C code, that the speedup was from checking the underlying collection, without advancing the iterator.  I presume that " ++it->it_index;" is the statement to the contrary. I should have either asked or found this sooner.  I unlinked the noisy comment.

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue31108>
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