Is there a standard class for an infinitely nested defaultdict?

Question

Does anyone know if there's a standard class for an infinitely nestable dictionary in Python?

I'm finding myself repeating this pattern:

d = defaultdict(lambda: defaultdict(lambda: defaultdict(int)))
d['abc']['def']['xyz'] += 1

If I want to add "another layer" (e.g. d['abc']['def']['xyz']['wrt']), I have to define another nesting of defaultdicts.

To generalize this pattern, I've written a simple class that overrides __getitem__ to automatically create the next nested dictionary.

e.g.

d = InfiniteDict(('count',0),('total',0))
d['abc']['def']['xyz'].count += 0.24
d['abc']['def']['xyz'].total += 1
d['abc']['def']['xyz']['wrt'].count += 0.143
d['abc']['def']['xyz']['wrt'].total += 1

However, does anyone know of a pre-existing implementation of this idea? I've tried Googling, but I'm not sure what this would be called.

Answer 1

I think this one-liner is a nearly perfect solution:

>>> from collections import defaultdict
>>> infinite_defaultdict = lambda: defaultdict(infinite_defaultdict)
>>> d = infinite_defaultdict() 
>>> d['x']['y']['z'] = 10

by Raymond Hettinger on Twitter (https://twitter.com/raymondh/status/343823801278140417)

Answer 2

This lends itself naturally to a recursive definition.

>>> import collections
>>> def nested_dd():
...     return collections.defaultdict(nested_dd)
...
>>> foo = nested_dd()
>>> foo
defaultdict(<function nested_dd at 0x023F0E30>, {})
>>> foo[1][2]=3
>>> foo[1]
defaultdict(<function nested_dd at 0x023F0E30>, {2: 3})
>>> foo[1][2]
3