On Mar 7, 1:19 pm, "Chris Mellon" <[EMAIL PROTECTED]> wrote: > On Fri, Mar 7, 2008 at 3:00 PM, DBak <[EMAIL PROTECTED]> wrote:
> > However I can't do this, because, of course, the name Tree isn't > > available at the time that the classes _MT and _Node are defined, so > > _MT and _Node can't inherit from Tree. > > Not only is the name not defined, the class doesn't even exist yet. Yes, but, well - it certainly isn't usable yet, but some object (that will be the class when it is finished) is being built (its __dict__ is being populated, etc.) - so there's an object pointer available inside the interpreter that could be put somewhere. But this is pedantic - you're right, the class really isn't available until after the class statement. > > What is the Pythonic thing I should be doing instead? > > Don't nest them. The single underscore is all you need to keep any > from using them (don't forget that even if your method worked, they'd > be perfectly visible as attributes of the Tree class, or as the types > of returned values). Worrying too much about visibility is a waste of > time in Python. Yes, I knew it wouldn't stop the determined coder from finding and using them. However, I did actually have a reason for wanted them nested: I wanted to put more than one similar data structure in the same source file - and several of them would have "Empty" nodes that would behave differently. If I used nested classes all those classes could be named Empty. If flattened to module level then I'd have to invent different names for each one, like, AVL_Empty, RedBlack_Empty, and it wouldn't seem as "nice" (for some definition of "nice" that I have in my head). > > (Easy answer: Put this code in a module, exposing only a factory > > function. I could do that, but wanted to know if I could encapsulate > > it as described so I could actually put several similar data > > structures into one module.) > > There's no reason to use a factory function. If you do put them in a > module, you can use __all__ to document your exports. As with all > visibility issues in Python, this is advisory only - the only code it > affects is the symbols that are exported by "from module import *". OK. Thanks! -- David -- http://mail.python.org/mailman/listinfo/python-list
