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shouldn't 'string'.find('ugh') return 0, not -1 ?

jelle feringa jelleferinga at gmail.com
Wed Oct 31 12:17:23 EDT 2007 
Thanks for your in-depth explanation Tim.
Which is impossible to disagree with!


On 10/31/07, Tim Chase <python.list at tim.thechases.com> wrote:
>
> > Well, I this is another idiom in itself, right?
> > Your checking if something is part of an iterable.
> > I'm checking truth before entering a conditional expression.
>
> I'm not sure I follow.  I simply replaced your
>
>   if check.find('something')
>
> with
>
>   if 'something' in check:
>
> which (1) is more readable (2) is more pythonic (especially as I
> understand that find() is going away), and (3) works like I
> understand you want from your description.
>
> For strings, they're the same behavior.  However, it also works
> for testing membership in other container classes (sets, lists,
> tuples, dicts, etc).
>
> Your original code's behavior would be analog to
>
>   if not check.startswith('something')
>
> which is not at all what I think you meant.  This
> misinterpretation alone is reason enough to give the find()
> method the boot.
>
> > The latter is considered to be pythonic, right?
>
> Clarity is pythonic.  The find() call returns an offset, or -1 if
> not found (because the beginning-of-string is offset=0).  It
> would also make sense if this returned None instead of -1.
> Either way, find() should be used for returning index values.  If
> you're testing for the presence of a substring, use the
>
>   if 'something' in check:
>
> to do the test.  And as for the start/end parameters to find,
> they are interpreted as slice endpoints, so
>
>   if check.find('something', start) != -1:
>
> would be the same as
>
>   if 'something' in check[start:]:
>
> and
>
>   if check.find('something', start, end) != -1:
>
> would be the same as
>
>   if 'something' in check[start:end]:
>
> both of which are far more readable than their find() variants.
>
> Hope this helps clarify,
>
> -tkc
>
>
>
>
>
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