Sebastian Linke added the comment:
@Josh
What is the point of using iterators here? If the user wants an iterator to be
checked then he can throw that iterator right away because it was exhausted by
the function. I think that in most cases the user wants to do some
postprocessing on a hairstack after being checked. This is why I restricted the
arguments to be sequences.
Keeping that restriction in mind a pure Python implementation could look like
this:
def has_subsequence(seq, subseq):
if not subseq:
return True
if len(subseq) > len(seq):
return False
start = 0
while True:
try:
start = seq.index(subseq[0], start)
except ValueError:
# seq.index() did not match
return False
stop = start + len(subseq)
if seq[stop - 1] == subseq[-1] and seq[start:stop] == subseq:
return True
start += 1
Unfortunately, this version potentially creates lots of subseqences for
checking equality with the `subseq` argument. I tried to minimise the
occurrence of those cases by pre-checking the first and the last element of a
candidate. Anyway, this seems to be faster for small needles compared to your
`deque`-based suggestion.
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<http://bugs.python.org/issue25898>
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