parameterized iterator?

[Fortepianissimo]

Just occurs to me that if I can somehow pass in an argument to specify
a special ordering when traversing a tree, that'll be perfect. A
simplified tree node iterator is something like this:

class Node:
  def __iter__ (self): return self.postorder()

  def postorder (self):
    if hasattr(self,daughters):
      for d in daughters:
        for dd in d: yield dd
    yield self


daughters is a list of the daughter nodes. This allows me to traverse
the tree in postorder:

for node in root:
  <do something to node>

Now I want to be able to slip in a new traversal generator to define
my own way of traversal. The only way I can think of is

def postorder (node):
  ...

def preorder (node):
  ...

tFunc=preorder  # change this if necessary

class Node:
  def __iter__ (self): return tFunc(self)


But then again 'tFunc' is immutable and if I change tFunc to another
traversal generator nothing would change! Unless I make tFunc a list
(mutable):

tFunc=[preorder]

and change and call tFunc[0] instead of tFunc. This is rather ugly. Is
there any better way to do this?


Thanks!