def iter_edges(self, cached_content=None):
if not cached_content:<EOL><INDENT>cached_content = self.get_cached_content()<EOL><DEDENT>all_leaves = cached_content[self]<EOL>for n, side1 in six.iteritems(cached_content):<EOL><INDENT>yield (side1, all_leaves - side1)<EOL><DEDENT>
Iterate over the list of edges of a tree. Each egde is represented as a
tuple of two elements, each containing the list of nodes separated by
the edge.