On 18 Aug, 21:50, Chris Rebert <c...@rebertia.com> wrote: > On Tue, Aug 18, 2009 at 10:09 AM, James > > Harris<james.harri...@googlemail.com> wrote: > > I am writing some code to form a tree of nodes of different types. The > > idea is to define one class per node type such as > > > class node_type_1(node): > > <specific properties by name including other node types> > > class node_type_2(node): > > <specific properties by name including other node types> > > etc > > > (Class "node" would hold any common properties). > > > When walking the tree I need to know what type of node I'm dealing > > with so polymorphism isn't generally useful. The action to be taken > > depends on the node type. > > I'm sure it relates to the exact type of tree you're walking and the > calculation you're doing on it, but what is the reason why your code, > which in the abstract sounds like it will vaguely resemble this: > > def walk_tree(tree): > if isinstance(tree, node_type_1): > #code > walk_tree(subtree) > elif isinstance(tree, node_type_2): > #code > walk_tree(subtree) > #etc... > > can't be written instead as: > > class node_type_1: > def walk_tree(self): > #code > self.subtree.walk() > > class node_type_2: > def walk_tree(self): > #code > self.subtree.walk() > > #etc
Interesting idea. This may be a better and a more OO solution than what I had in mind. I'm not sure if I can use this but I'll see how it fits in as the work progresses. The tree is for a compiler. Initially the tree is for parsing of source code. Then it will need to be processed and changed as further compiler phases are written. I don't know yet whether it will be easier to modify the tree or to create a new one for each phase. So I guess whether I use the idea depends on the commonality of operations. James -- http://mail.python.org/mailman/listinfo/python-list
