How to Create an Infinitely-Nested defaultdict in Python?

How to Create an Infinite-Level Recursive defaultdict

Python's defaultdict is a versatile data structure that can be used to create nested dictionaries. However, by default, defaultdicts only provide a single level of nesting. Is there a way to create a defaultdict that behaves as the default factory for inner defaultdicts, effectively creating an infinite-level recursive structure?

The original question sought to achieve the following behavior:

x = defaultdict(...stuff...)
x[0][1][0]
# Should return an empty dictionary {}

Using only the native defaultdict arguments, it is not possible to create an infinitely-nested recursive defaultdict. The popular workaround is to utilize a lambda function:

x = defaultdict(lambda: defaultdict(dict))

This approach creates a defaultdict that generates a new defaultdict when accessing a missing key. This effectively provides infinite levels of nesting.

Advantages of the Lambda-Based Approach:

• Explicit and Understandable: The syntax clearly defines the desired behavior, making it easy for other developers to comprehend.
• Flexible Data Types: The "leaf" of the defaultdict can be customized to be a list, set, or any other data structure by modifying the lambda function.

Note:

The infinitely-nested defaultdict using lambda has the following characteristics:

• Accessing a missing key will always return a new instance of the specified data type (in this case, a defaultdict(dict)).
• The nesting depth is technically bounded by the available memory and the specific data structure used (in this case, a defaultdict(dict)).

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