Can You Freeze a Dictionary in Python?

Is a "Frozen Dict" Possible in Python?

The concept of a "frozen dict" has been a topic of discussion within the Python community. While Python doesn't provide a built-in frozendict, several solutions have emerged to address the need for an immutable, hashable dictionary.

One common reason for wanting a frozen dict is to memoize function calls with unknown arguments. A typical approach involves converting the arguments into a tuple using tuple(sorted(kwargs.items())), relying on sorting stability for hash table lookup.

For a more comprehensive approach, consider the following FrozenDict class:

<code class="python">import collections

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

This class provides methods for iteration, length determination, item retrieval, and hash calculation, ensuring it behaves like a standard dictionary and supports hashing.

In practice, the FrozenDict operates efficiently:

<code class="python">x = FrozenDict(a=1, b=2)
y = FrozenDict(a=1, b=2)
print(x is y, x == y, x == {'a': 1, 'b': 2})
d = {x: 'foo'}
print(d[y])  # 'foo'</code>

By providing a custom implementation, the FrozenDict allows for immutable, hashable dictionaries in Python, extending the possibilities for object handling and memory optimization.

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