Oops, messed this up (too late to edit). Thanks choochootrain for the correction: >>> NestedDD = lambda: collections.defaultdict(NestedDD) >>> nested_dd =

Oops, messed this up (too late to edit). Thanks choochootrain for the correction: >>> NestedDD = lambda: collections.defaultdict(NestedDD) >>> nested_dd = NestedDD() >>> nested_dd['a']['b']['c']['d'] = 'hello' does the proper thing.