Ah - I have been very silly indeed! I had not realised that by creating my lists outside of the def__init___() constructor they would always be class rather than instance variables, and so there was only one of them when I referred to it. Thanks to Erik and Chris for your help!
Ben Ben wrote: > Ah - ok. In fact I simply had: > > class record: > my_list =[] > mops=[] > > def __init__(self,mops): > self.mops=mops > > Where mops is something I pass in when i create the instance. I had > thought that then each time I created an instance of the record class > as an element of my dictionary: > > self.mop_list[record_number]=record(self.mops[:]) > > I would create a brand new instance of the record class.It would have a > mops list initialized with mops (because the def__init__ constructor is > called when the class is instantiated), and an empty, individual list > my_list. > > I could then access each individual list by doing: > > self.mop_list[x].my_list[y]=something > > But in fact the same my_list is being accessed for all values of x, so > a change to one list is in fact a change to them all. I think you might > be right, but can't quite work it out myself! I'll keep trying :-) > > Thanks for your help, > > Ben > > > > > > Erik Johnson wrote: > > > "Ben" <[EMAIL PROTECTED]> wrote in message > > news:[EMAIL PROTECTED] > > > > <snip> > > > > > This seems to work without any errors. But bizzarely I find that > > > whatever my record number, the instance of "my_class" is appended to > > > every list. So in this case > > > > > > self.mop_list[0].my_list.append(my_class(Some data for the > > > constructor)) > > > > > > I would expect to append an instance of my_class to > > > self.mop_list[0].my_list > > > > > > But annoyingly > > > > > > self.mop_list[0].my_list > > > self.mop_list[3].my_list > > > self.mop_list[7].my_list > > > > > > all have an instance of my_class created and appended to them. This is > > > really confusing and quite annoying - I don't know whether anyone out > > > there can make head or tail of what I'm doing wrong? > > > > Well, it's a little bit difficult, but I think I actually know what's going > > on. You probably need some code that looks something like this, to ensure > > each object has it's own, independent list: > > > > class record: > > def __init__(self, init_list=None): > > self.my_list = [] > > if init_list is not None: > > self.my_list.extend(init_list) > > > > > > Here's what I think you are doing, and below should make it clear why that > > doesn't work: > > > > class record: > > def __init__(self, init_list=[]): > > > > That list above, the default initializer is constructed just once (when the > > def statement executes)! > > > > >>> class record: > > ... def __init__(self, init_list=[]): > > ... self.my_list = init_list > > ... > > >>> r1 = record() > > >>> r1.my_list > > [] > > >>> r2 = record() > > >>> r2.my_list > > [] > > >>> r2.my_list.append('boo!') > > >>> r1.my_list > > ['boo!'] > > >>> > > >>> l1 = range(1, 4) > > >>> l1 > > [1, 2, 3] > > >>> r1 = record(l1) > > >>> r2 = record(l1) > > >>> r1.my_list > > [1, 2, 3] > > >>> r2.my_list > > [1, 2, 3] > > >>> r1.my_list.append(42) > > >>> l1 > > [1, 2, 3, 42] > > >>> r1.my_list > > [1, 2, 3, 42] > > >>> r2.my_list > > [1, 2, 3, 42] > > >>> -- http://mail.python.org/mailman/listinfo/python-list
