Martin v. Löwis wrote: > daniel wrote: > > when I tried to check the stuff out, found sth interesting that if you > > define variables in a style like this: > > a = b = ['a', 'b'] > > changing one list affects the other, and they still refer to same > > object. in fact, seems all compound types (dictionary for instance) > > behave in this way. > > > > however, when list is replaced with other built-in types like integers > > : > > a = b = 3 > > changing one of them cause the two objects differ... > > Ah, but make a difference between "change a variable", and "change an > object". > > py> a = b = [1,2,3] > py> a[0] = 6 # don't change the variable a, just change the object > py> a > [6, 2, 3] > py> b > [6, 2, 3] > py> a=[7,8,9] # change the variable a; > # it's now a different object than b mm, python runtime might allocate a new chunk of memory for this... but might not for the previous operation.. > py> a > [7, 8, 9] > py> b > [6, 2, 3] > > For some objects, "change the object" is impossible. If you have > > a = b = 3 > > then there is no way to change the object 3 to become 4 (say); > integer objects are "immutable". So for these, to make a change, > you really have to change the variable, not the value. > sounds reasonable, I tried tuple which is also immutable, it behaves the same as integers.
> Regards, > Martin tks Martin... -- http://mail.python.org/mailman/listinfo/python-list
