On May 20, 10:42 am, John Salerno <[EMAIL PROTECTED]> wrote: > On Mon, 19 May 2008 20:34:22 -0700 (PDT) > > [EMAIL PROTECTED] wrote: > > i am confused. > > > x=5 > > y=5 > > > x==y -> True > > x is y -> True > > > shouldnt x is y return False since they shouldnt(dont?) point to the > > same place in memory, they just store an equal value? > > For some immutable values (such as numbers and strings), Python will have > separate variables reference the same object, as an optimization. This > doesn't affect anything, since the numbers are immutable anyway and a shared > reference won't create any unexpected changes. > > It also works with small, but not large, strings: > > > > >>> x = 'hello' > >>> y = 'hello' > >>> x == y > True > >>> x is y > True > >>> a = 'this is longer' > >>> b = 'this is longer' > >>> a == b > True > >>> a is b > False > > In the above example, Python has created only one string called 'hello' and > both x and y reference it. However, 'this is longer' is two completely > different objects.
But the rule of thumb is: Don't rely on this optimization, it's an implementation detail. -- http://mail.python.org/mailman/listinfo/python-list
