python iterator through tree with list of children

i don't get the full grasp on python iterators, i got an object with a list of children, and i want to iterate through this structure. I want to get the same behaviour as with the printall function but with an iterator.

    class t:
            def __init__(self, i):
                    self.l = []
                    self.a = 0
                    for ii in range(i):
                            self.a = ii
                            self.l.append(t(i-1))

            def __iter__(self):
                    return self

            def next(self):
                    for i in self.l:
                            yield i.__iter__()
                    yield self

            def printall(self):
                    for i in self.l:
                            i.printall()
                    print self.a

hope thats enough information, thanks

edit:

i just want to be able to iterate through all the leafs of the tree and do something with the object, i.e. when i have an instance

    bla = t(3) 

i want to be able to go through every node with

    for x in bla:
            print x.a

for example. i want to be able to something with each x, i just have to access every child once