On Mar 6, 12:23 pm, Gary Herron <gher...@islandtraining.com> wrote: > Robert Kern wrote: > > On 2009-03-06 13:46, Gary Herron wrote: > >> Emanuele D'Arrigo wrote: > >>> Hi everybody, > > >>> while testing a module today I stumbled on something that I can work > >>> around but I don't quite understand. > > >> *Do NOT use "is" to compare immutable types.* **Ever! ** > > > Well, "foo is None" is actually recommended practice.... > > But since newbies are always falling into this trap, it is still a good > rule to say: > > Newbies: Never use "is" to compare immutable types.
No it isn't, it's asinine advice that's not even a simpllified truth, it's just a lie. Newbies who don't understand the difference between "==" and "is" should not be using "is", for any object, immutable or mutable, aside from None (which, whether you like it or not, is idomatic Python). Everyone who's learned the difference between equality and same identity, including experts, should be using "is" only to test if some object is the same object they created themselves, or is an object guaranteed by a library or the langauge to never change, irrespective of whether the object is mutable or not. At no point on the learning curve is the distinction of when to use "is" or not ever mutability. Carl Banks -- http://mail.python.org/mailman/listinfo/python-list
