On Wed, Dec 23, 2015 at 11:46 PM, Neal Becker <ndbeck...@gmail.com> wrote: > I'm a bit surprised that an object() can't have attributes: > > In [30]: o = object() > > In [31]: o.x = 2 > --------------------------------------------------------------------------- > AttributeError Traceback (most recent call last) > <ipython-input-31-815c47907397> in <module>() > ----> 1 o.x = 2 > > AttributeError: 'object' object has no attribute 'x'
BTW, the reason for this is that the base 'object' type doesn't have a __dict__. When you create a subclass, you get a __dict__ by default; but you can override this. $ python3 Python 3.6.0a0 (default:6e114c4023f5, Dec 20 2015, 19:15:28) [GCC 4.9.2] on linux Type "help", "copyright", "credits" or "license" for more information. >>> object().__dict__ Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: 'object' object has no attribute '__dict__' >>> import sys >>> class NS(object): pass ... >>> class empty(object): __slots__ = () ... >>> sys.getsizeof(object()) 16 >>> sys.getsizeof(NS()) 56 >>> sys.getsizeof(empty()) 16 The cost of supporting arbitrary attributes is significant. It's common enough in custom classes that you have to explicitly ask for the cut-down version, but when all you need is a sentinel, that's a slab of memory and functionality that you just don't need, so it's not there. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
