On Thu, 12 Aug 2010 19:52:07 -0700, Matt Schinckel wrote: >>>> a = "hello" >>>> b = "hello" >>>> a is b > True > > Ooh, that looks dangerous. Are they the same object?
You don't need another test to know that they are the same object. The `is` operator does exactly that: a is b *only* if a and b are the same object. >>>> a += "o" >>>> a > 'helloo' >>>> b > 'hello' > > Phew. This tests for mutability, not sameness. If strings were mutable, then modifying a in place would likewise cause b to be modified (because they are the same object). Here's an example: >>> a = b = [1, 2, 3] >>> a is b True >>> a += [4] >>> b [1, 2, 3, 4] But of course, if strings were mutable like lists, they wouldn't be cached! The consequences would be horrific if they were, unless Python's execution model were radically different. Copy-on-write perhaps? > (Python does not make two copies of small strings until it needs to). Python doesn't copy anything unless you ask it to. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
