tjreedy at udel.edu
Tue Jul 8 03:22:04 CEST 2008
David C. Ullrich wrote:
>>>> 'ab' in 'abc'
'a' in 'abc' works according to the standard meaning of o in collection.
'ab' in 'abc' could not work by that standard meaning because strings,
as virtual sequences, only contain characters (length 1 strings). Among
built-in collections, this limitation is unique to strings (and bytes,
in 3.0). So in 2.3, 'in' was given a useful extension of meaning that
is also unique to strings (and bytes).
>>>> [1,2] in [1,2,3]
[1,2] can be an member of tuples, lists, dicts and other general
collections. [1,2] in collection therefore has that meaning, that it is
a single element of collection. Extending the meaning would conflict
with this basic meaning.
> Is there a reason for the inconsistency? I would
> have thought "in" would check for elements of a
> sequence, regardless of what sort of sequence it was...
It is not an inconsistency but an extension corresponding to the
limitation of what an string element can be.
Terry J. Reedy
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