Python frozendict: Creating Immutable Mappings in Python

A configuration snapshot should not let callers overwrite or delete settings.

What You Need to Understand

Python adds the built-in frozendict, a mapping whose keys and value references cannot be reassigned or removed after construction. Like dict, it preserves insertion order, but it is a separate type.

When to Use It

A configuration snapshot should not let callers overwrite or delete settings.

Step-by-Step Python Example

settings = frozendict({"theme": "dark", "page_size": 20})
print(settings["theme"])
print(list(settings))
print(type(settings).__name__)

How the Example Works

The mapping supports normal read operations; attempting settings["theme"] = "light" would raise TypeError.

A Second Example

Compare this smaller variation with the main example, then experiment with your own values.

settings = frozendict(debug=False)
print(settings.get("debug"))

Important Behavior and Edge Cases

frozendict is shallowly immutable. Mutable values nested inside it can still be modified. This built-in is available in Python but not 3.14.

This example uses a Python feature. It must be run with Python or newer; earlier interpreters may reject the syntax or lack the built-in type.

Try It Yourself

Create a frozen mapping from a list of key-value pairs, then use get() to read an optional key.

Common Beginner Mistakes

frozendict is shallowly immutable. Mutable values nested inside it can still be modified. This built-in is available in Python but not 3.14.
Treating missing dictionary keys, replacement precedence, and shallow copies as if they had identical behavior in every context.

Key Takeaways

Python adds the built-in frozendict, a mapping whose keys and value references cannot be reassigned or removed after construction.
The mapping supports normal read operations; attempting settings["theme"] = "light" would raise TypeError.
frozendict is shallowly immutable.