On Jun 13, 11:38 am, Mike Kent <[EMAIL PROTECTED]> wrote: > For Python 2.5 and new-style classes, what special method is called > for mylist[2:4] = seq and for del mylist[2:4] (given that mylist is a > list, and seq is some sequence)? > > I'm trying to subclass list, and I'm having trouble determining what > special methods I have to override in my class for the above two > operations. From my testing, it seems to be __setslice__ for both, > but the docs say __setslice__ and brethren are deprecated. I would > have thought that __setitem__ and __delitem__ would be what was > called, but again, my testing says otherwise.
It is a combination. http://docs.python.org/ref/sequence-methods.html For setting a slice in the form `x[from:to] = seq` the __setslice__ method will be called if it exists: x.__setslice__(from, to, seq) if __setslice__ doesn't exists __setitem__ is called with a slice object: x.__setitem__(slice(from,to), seq) if setting a slice in the form `x[from:to:step] = seq` (extended slicing) __setitem__ will be called with a slice object: x.__setitem__(slice(from, to, step), seq) For non slices (single index values) __setitem__ is always called. The real problem, and someone correct me if I'm wrong (this is a newsgroup... of course they will :p), is that you can't make your class hide or get rid of __setslice__ on the base class. I've tried making __getattribute__ raise an AttributeError and making __hasattr__ return False, neither works. I think this is because list is implemented in C and the __setslice__ slot is filled. Because the list object is implemented in C and is optimized, it doesn't use __getattribute__ or __hasattr__ to find out if the slice method exists, Python just grabs the pointer from the c structure and uses it. In my examples I only mentioned __setslice__/__setitem__, but all the same should apply to __delslice__/__delitem__ as well. So, it looks like as long as you want to subclass list, you are stuck implementing both __*slice__ and __*item__ methods. Matt -- http://mail.python.org/mailman/listinfo/python-list
