The following Python tree structure recently resurfaced. I find it rare to see functional or recursive techniques expressed so succinctly in Python:
def tree(): return collections.defaultdict(tree)
Another construction I am quite fond of is:
for _, dirnames, filenames in os.walk(path): break
...which leaves dirnames and filenames in the current scope, containing the immediate subdirectories and files of the specified path.
Perhaps a little too cute, but appealing in its own way.