En Tue, 17 Jun 2008 02:25:42 -0300, Lie <[EMAIL PROTECTED]> escribió: > On Jun 17, 11:07 am, "Leo Jay" <[EMAIL PROTECTED]> wrote: >> On Tue, Jun 17, 2008 at 11:29 AM, pirata <[EMAIL PROTECTED]> wrote:
>> > What's the difference between "is not" and "!=" or they are the same thing? >> >> The 'is' is used to test do they point to the exactly same object. >> The '==' is used to test are their values equal. >> >> and be very careful to the dirty corner of python: [example with "5 is 5" but "100000 is not 100000"] > No you don't have to be careful, you should never rely on it in the > first place. > > Basically 'a is b' and 'not(a is b)' is similar to 'id(a) == id(b)' > and 'not(id(a) == id(b))' No. > You use 'is' when you want to test whether two variable/names are > actually the same thing (whether they actually refers to the same spot > on memory). The '==' equality comparison just test whether two > objects' values can be considered equal. Yes, *that* is true. The above statement is not. A counterexample: py> [] is [] False py> id([])==id([]) True Even dissimilar objects may have the same id: py> class A: pass ... py> class B: pass ... py> A() is B() False py> A() == B() False py> id(A())==id(B()) True Comparing id(a) with id(b) is only meaningful when a and b are both alive at the same time. If their lifetimes don't overlap, id(a) and id(b) are not related in any way. So I think that trying to explain object identity in terms of the id function is a mistake. -- Gabriel Genellina -- http://mail.python.org/mailman/listinfo/python-list
