Can a defaultdict Recursively Serve as its Own Default Value for Infinite Nesting?

Creating an Infinitely Nested defaultdict of defaultdict

Question:

Is it possible to create a defaultdict that also serves as the default value for itself, resulting in an infinite-level recursive defaultdict? The goal is to enable access to deeply nested elements without encountering KeyError exceptions.

Answer:

While the other answers address the creation of "infinitely many" nested defaultdicts, they overlook the specific need for a two-depth defaultdict. To achieve this, the following code can be used:

defaultdict(lambda: defaultdict(dict))

This construct provides the following advantages:

• Explicitness: It is more straightforward and understandable than the recursive approach.
• Customizable Leaf: It allows for the customization of the "leaf" value of the defaultdict to be something other than a dictionary, such as lists or sets.

Example:

x = defaultdict(lambda: defaultdict(dict))
x[0][1][0]
{}  # returns an empty dictionary

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