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Groups > comp.lang.python > #33735

Re: Inconsistent behaviour os str.find/str.index when providing optional parameters

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On 2012-11-21 12:43, Giacomo Alzetta wrote:
> I just came across this:
>
>>>> 'spam'.find('', 5)
> -1
>
>
> Now, reading find's documentation:
>
>>>> print(str.find.__doc__)
> S.find(sub [,start [,end]]) -> int
>
> Return the lowest index in S where substring sub is found,
> such that sub is contained within S[start:end].  Optional
> arguments start and end are interpreted as in slice notation.
>
> Return -1 on failure.
>
> Now, the empty string is a substring of every string so how can find fail?
> find, from the doc, should be generally be equivalent to S[start:end].find(substring) + start, except if the substring is not found but since the empty string is a substring of the empty string it should never fail.
>
[snip]
I think that returning -1 is correct (as far as returning -1 instead of
raising an exception like .index could be considered correct!) because
otherwise it whould be returning a non-existent index. For the string
"spam", the range is 0..4.

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Inconsistent behaviour os str.find/str.index when providing optional parameters Giacomo Alzetta <giacomo.alzetta@gmail.com> - 2012-11-21 04:43 -0800
  Re: Inconsistent behaviour os str.find/str.index when providing optional parameters MRAB <python@mrabarnett.plus.com> - 2012-11-21 13:32 +0000
  Re: Inconsistent behaviour os str.find/str.index when providing optional parameters Alister <alister.ware@ntlworld.com> - 2012-11-21 16:59 +0000
    Re: Inconsistent behaviour os str.find/str.index when providing optional parameters Hans Mulder <hansmu@xs4all.nl> - 2012-11-21 20:25 +0100
      Re: Inconsistent behaviour os str.find/str.index when providing optional parameters Giacomo Alzetta <giacomo.alzetta@gmail.com> - 2012-11-21 12:21 -0800
      Re: Inconsistent behaviour os str.find/str.index when providing optional parameters MRAB <python@mrabarnett.plus.com> - 2012-11-21 20:58 +0000
  Re: Inconsistent behaviour os str.find/str.index when providing optional parameters Terry Reedy <tjreedy@udel.edu> - 2012-11-21 22:41 -0500
  Re: Inconsistent behaviour os str.find/str.index when providing optional parameters MRAB <python@mrabarnett.plus.com> - 2012-11-22 04:00 +0000
    Re: Inconsistent behaviour os str.find/str.index when providing optional parameters Giacomo Alzetta <giacomo.alzetta@gmail.com> - 2012-11-21 23:01 -0800
      Re: Inconsistent behaviour os str.find/str.index when providing optional parameters Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-11-22 08:44 +0000
        Re: Inconsistent behaviour os str.find/str.index when providing optional parameters Giacomo Alzetta <giacomo.alzetta@gmail.com> - 2012-11-22 10:22 -0800
    Re: Inconsistent behaviour os str.find/str.index when providing optional parameters Giacomo Alzetta <giacomo.alzetta@gmail.com> - 2012-11-21 23:01 -0800

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