'<char> in <string>' works, why doesnt '<string> in <string>'?

[Tim Roberts]

morton at dennisinter.com (damien  morton) wrote:

>Ok, I see how this works. 
>
>'<string1> in <string2>' would always returns false; as the elements
>of a <string2> are all characters you can never find <string1> amongst
>them (unless its a string of length 1).
>
>Its counter-intuitive for someone playing with strings as strings
>rather than as sequences of characters, however.

Many things that are "intuitive" are also wrong.

>'c' in 'the quick brown fox'     -> 1
>'fox' in 'the quick brown fox'   -> 1 (instead of TypeError)
>
>Is there any circumstance where youd expect (or want) the later not to
>work? I expected and wanted it to work (but instead got an error), its
>quite a clear and unambiguous expression (for strings only).

It would be a clear and unambiguous expression _if_ the "in" operator was a
substring search operator, but it is not.  It is a set membership operator.
It works EXACTLY the same way on all sequence types: the right-hand operand
is a sequence, and the left-hand operand is something that can be an
element of that sequence type.  You are suggesting an unorthogonal change
just because it is easier to type than:

   'the quick brown fox'.find('fox')

No.  That is NOT a good reason to change a language in an inconsistent way.
--
- Tim Roberts, timr at probo.com
  Providenza & Boekelheide, Inc.