On Fri, 31 Oct 2008 16:02:53 +0000, Duncan Booth wrote: > [EMAIL PROTECTED] wrote: > >>> x = 1 >>> y = x # does assignment make copies? y += 1 >>> assert x == 1 >>> => succeeds, which implies that Python makes a copy when assigning >> >> with lists: >> >>> x = [1] >>> y = x # does assignment make copies? y += [1] >>> assert x == [1] >>> => fails, which implies that Python uses references when assigning >> >> Compare lists with tupels: >> >> x = (1,) >> y = x # does assignment make copies? y += (1,) >> assert x == (1,) >>=> succeeds, which implies *what*? > > All any of this does is 'implies that += may create a new object or may > mutate an existing object. RTFM: Python Reference Manual 6.3.1
The exact test isn't important. If you don't like those tests, replace them with something else: y = y + [1] perhaps, or y.sort(), or whatever you like. Naturally you will get different results according to whatever specific test you try, and the interpretation of those results will therefore be different. But no matter what tests are done, somebody who fails to understand Python's calling model (or if you prefer, its assignment model) will wrongly interpret the results they see in terms of a model they do understand. Because call by reference and call by value are such older and established models, and used in such historically popular languages like C and Pascal, they are the most likely incorrect assumptions people will start from. -- Steven -- http://mail.python.org/mailman/listinfo/python-list
