I'm having a hard time coming up with a reasonable way to explain certain things to programming novices.
Consider the following interaction sequence: >>> def eggs(some_int, some_list, some_tuple): ... some_int += 2 ... some_list += [2] ... some_tuple += (2,) ... >>> x = 42 >>> y = (42,) >>> z = [42] >>> eggs(x, y, z) >>> x 42 >>> y (42,) >>> z [42, 2] >>> How do I explain to rank beginners (no programming experience at all) why x and y remain unchanged above, but not z? Or consider this one: >>> ham = [1, 2, 3, 4] >>> spam = (ham,) >>> spam ([1, 2, 3, 4],) >>> spam[0] is ham True >>> spam[0] += [5] Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: 'tuple' object does not support item assignment >>> ham += [5] >>> spam ([1, 2, 3, 4, 5, 5],) >>> What do you say to that? I can come up with much mumbling about pointers and stacks and heaps and much hand-waving about the underlying this-and-that, but nothing that sounds even remotely illuminating. Your suggestions would be much appreciated! TIA! kj -- http://mail.python.org/mailman/listinfo/python-list
