Faheem Mitha wrote:
On Wed, 18 Jun 2008 12:57:44 -0700 (PDT), Lie <[EMAIL PROTECTED]> wrote:
On Jun 19, 2:26 am, Faheem Mitha <[EMAIL PROTECTED]> wrote:
Hi everybody,
I was wondering if anyone can explain this. My understanding is that 'is'
checks if the object is the same. However, in that case, why this
inconsistency for short strings? I would expect a 'False' for all three
comparisons. This is reproducible across two different machines, so it is
not just a local quirk. I'm running Debian etch with Python 2.4.4 (the
default).
Thanks, Faheem.
In [1]: a = '--'
In [2]: a is '--'
Out[2]: False
In [4]: a = '-'
In [5]: a is '-'
Out[5]: True
In [6]: a = 'foo'
In [7]: a is 'foo'
Out[7]: True
Yes, this happens because of small objects caching. When small
integers or short strings are created, there are possibility that they
might refer to the same objects behind-the-scene. Don't rely on this
behavior.
Yes, but why is '-' and 'foo' cached, and not '--'? Do you know what
the basis of the choice is?
Shortish Python identifiers and operators, I think. Plus a handful like '\x00'.
The source would know for sure, but alas, I am lazy.
--
Robert Kern
"I have come to believe that the whole world is an enigma, a harmless enigma
that is made terrible by our own mad attempt to interpret it as though it had
an underlying truth."
-- Umberto Eco
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