Two-level breadth-first descent using a generator

gistfile1.py

     # Generators leave it up to the caller whether
     # to build a list, or set, or maybe just to
     # loop and not build a data structure at all:

     def get_children(self):
          for c in self.children.itervalues():
              yield c
          for c in self.children.itervalues():
              for c2 in c.get_children():
                  yield c2

...
    # Then, later:

    children = list(obj.get_children())

    # Yes, it was finicky of me to use itervalues()
    # but if I am going to illustrate zero-data-
    # structure iteration, then I might as well go
    # the whole way.