Ulrich Eckhardt wrote: > Peter Otten wrote: >> Examples for classes that don't accept attributes are builtins >> like int, tuple, and -- obviously -- dict. You can make your own >> using the __slot__ mechanism: >> >>>>> class A(object): >> ... __slots__ = ["x", "y"] >> ... >>>>> a = A() >>>>> a.x = 42 >>>>> a.y = "yadda" >>>>> a.z = 123 >> Traceback (most recent call last): >> File "<stdin>", line 1, in <module> >> AttributeError: 'A' object has no attribute 'z' > > Wow. This is something I've been missing dearly in my toolbox until now! > Typically, when in C++ I would have used a struct, I always created a > class that set the according attributes in the init function instead, > which is quite a bit more cumbersome. Or I used a tuple and hoped to get > the position of the elements correct. > > Now, follow-up question: > 1. The slots are initialized to None, right? Or are they just reserved? > IOW, would "print a.x" right after creation of the object print anything > or raise an AttributeError? > > 2. Is there a convenient syntax to init an instance of such a class? Can I > convert it from e.g. a dict or do I still have to write a constructor or > manually fill in the slots?
collections.namedtuple is a convenient struct replacement -- if you don't mind that it is immutable. -- http://mail.python.org/mailman/listinfo/python-list
