What is a \"Frozen Dictionary\" in Python and How is it Implemented?

What is a "Frozen Dictionary"?

Python lacks an explicit concept of a "frozen dictionary." However, the following are some considerations related to the concept:

Proposed Implementation

Despite the lack of a builtin implementation, one can create a wrapper class to mimic a frozen dictionary:

<code class="python">import collections

class FrozenDict(collections.Mapping):
    ...</code>

This class provides the necessary methods and properties to function like a dictionary, but prohibits modifications.

Hashing

A frozen dictionary should support hashing, allowing it to be used as a key in other dictionaries or sets. The class implementation above incorporates a custom hashing function to provide this functionality.

Uses

A frozen dictionary is useful in situations where memoization is required. By freezing the dictionary, it can be used as a hashable key to store the results of a function with arbitrary arguments.

Comparison to Tuples

Frozen dictionaries are distinct from tuples (immutable lists) in that they support key-value operations. Tuples provide key indexing, but lack the ability to set or retrieve values.

Note

Python now includes a built-in frozen dict type that can be used in place of the custom implementation described above. It was introduced in PEP-603 and offers enhanced performance and correctness.

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