[Python-ideas] FInd first tuple argument for str.find and str.index

Mathias Panzenböck grosser.meister.morti at gmx.net
Wed Sep 5 18:50:21 CEST 2007

Terry Jones wrote:
>>>>>> "Guido" == Guido van Rossum <guido at python.org> writes:
> Guido> I was surprised to find that startswith and endswith support this,
> Guido> but it does make sense. Adding a patch to 2.6 would cause it to be
> Guido> merged into 3.0 soon enough.
> Guido> On 9/4/07, Ron Adam <rrr at ronadam.com> wrote:
>>> Could we add the ability of str.index and str.find to accept a tuple as the
>>> first argument and return the index of the first item found in it.
> Hi
> If someone is going to head down this path, it might be better to implement
> a more general algorithm and provide the above as a special case via an
> argument.
> There's a fast and beautiful algorithm due to Aho & Corasick (CACM, 1975)
> that finds _all_ matches of a set of patterns. It runs in time that's
> linear in max(sum of the lengths of the patterns to be matched, length of
> to-be-matched text). The algorithm was the basis of fgrep.
> To provide the above, a special case could have it return as soon as it
> found a first match (i.e., of any pattern).
> One general way to write it would be to have it return a dict of patterns
> and result indices in the case that the pattern argument is a tuple.
> So
>   "Hey, look, look, look at these patterns".find(('look', 'for', 'these', 'patterns'))
> might return
>     {
>       'look'     : [ 5, 11, 17 ],
>       'for'      : [ ],  # or arguably [ -1 ],
>       'these'    : [ 25 ],
>       'patterns' : [ 31 ],
>     }
> OK, that's a bit of a departure from the normal behavior of find, but so is
> passing a tuple of patterns. Alternately, you could also get back a tuple
> of (tuples of) matching indices.
> The ideal calling interface and result depends on what you need to do -
> check if a specific string matched? Just know the first match offset, etc.
> I don't know the best solution, but the algorithm rocks. Raymond - you'll
> love it :-)
> Terry

I would expect such a method to return the index where one of the given strings was
found. Or maybe a tuple: (start, end) or a tuple: (start, searchstring).


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