Many thanks Emile, Bob, Stefan, Wesley!
Now, I see now that the point is more related to implementation details
and optimization instead of a true
property. But it could mistaken people not aware.
Regards
Karim
On 01/10/2011 06:56 PM, Stefan Behnel wrote:
Karim, 10.01.2011 17:07:
I am not a beginner in Python language but I discovered a hidden
property
of immutable elements as Numbers and Strings.
s ='xyz'
>>> t = str('xyz')
>>> id(s) == id(t)
True
Thus if I create 2 different instances of string if the string is
identical (numerically). I get the same object in py db. It could be
evident but if I do the same (same elements) with a list it will not
give the same result. Is-it because of immutable property of strings and
numbers?
AFAIR, all string literals in a module are interned by the CPython
compiler, and short strings that look like identifiers are also
interned (to speed up dictionary lookups, e.g. for function names). So
you will get identical objects in these cases, although it's not a
good idea to rely on this as it's an implementation detail of the
runtime.
And the second thing that you can observe here is that str() never
copies a string you pass in, which is reasonable behaviour for
immutable objects.
Thus if I create 2 different instances of string if the string is
identical (numerically).
There's no such thing as "numerically identical" strings. It's enough
to say that they are identical as opposed to equal.
Stefan
_______________________________________________
Tutor maillist - Tutor@python.org
To unsubscribe or change subscription options:
http://mail.python.org/mailman/listinfo/tutor
_______________________________________________
Tutor maillist - Tutor@python.org
To unsubscribe or change subscription options:
http://mail.python.org/mailman/listinfo/tutor
