Josh Rosenberg added the comment:
A utility like this seems like it would belong in `itertools`, not
`collections`. It should also ideally avoid fully realizing the sequence so it
could work with iterators/generators as well; PySequence_Fast will force
creation of a `list`/`tuple` of the whole sequence when in practice, a `deque`
with a maxlen could be used to only maintain the necessary window into the
"haystack".
It would also help to have a pure Python implementation (and until you have
one, it's probably overkill to write the C accelerator) for other Python
distributions, and to serve as a baseline for comparison to see if a C
accelerator is justified. Something like this might be a decent point of
comparison:
def has_subsequence(it, searchseq, *, all=all, map=map, eq=operator.eq):
searchseq = tuple(searchseq)
if not searchseq:
return True # Empty sequence in everything
window = collections.deque(itertools.islice(it, len(searchseq)-1),
len(searchseq))
for x in it:
window.append(x)
if all(map(eq, window, searchseq)):
return True
return False
----------
nosy: +josh.r
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<http://bugs.python.org/issue25898>
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