string identity and comparison

[André]

On Thursday, December 16, 2010 7:55:20 AM UTC-4, jeanmichel wrote:
> Fellows,
> 
> I'd like to illutrate the fact that comparing strings using identity is, 
> most of the time, a bad idea. However I'm searching a short example of 
> code that yields 2 differents object for the same string content.
> 
> id('foo')
> 3082385472L
> id('foo')
> 3082385472L
> 
> Anyone has that kind of code ?
> 
> JM

How about this:

Python 2.6 (trunk:66714:66715M, Oct  1 2008, 18:36:04) 
[GCC 4.0.1 (Apple Computer, Inc. build 5370)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> a = 'spam'
>>> b = 'spa'
>>> c = a[:-1]
>>> c
'spa'
>>> id(c)
548256
>>> id(b)
548224

Or, even more simply, this:

Jython 2.5.0 (Release_2_5_0:6476, Jun 16 2009, 13:33:26) 
[Java HotSpot(TM) Client VM (Apple Inc.)] on java1.5.0_26
Type "help", "copyright", "credits" or "license" for more information.
>>> a = 'foo'
>>> b = 'foo'
>>> id(a)
1
>>> id(b)
2

Reusing immutable objects, for the sake of efficiency, is an implementation details which should not be relied upon (as you know since you ask for examples).

André