Python immutable dict

Basically, Python dictionary data structures mean you can modify the contents of a dictionary by adding, deleting, or changing its key-value pairs. Using types.MappingProxyType you can create an immutable dict in Python.

from types import MappingProxyType

power_levels = MappingProxyType(
    {
        "Kevin": 9001,
        "Benny": 8000,
    }
)

The MappingProxyType function takes a dictionary as an argument and returns a new object that behaves like a read-only view of the original dictionary.

Python immutable dict example

Simple example code immutable dictionary using the MappingProxyType function:

import types

original_dict = {'name': 'John', 'age': 25}
immutable_dict = types.MappingProxyType(original_dict)
print(immutable_dict)

# modify the immutable dictionary
immutable_dict['name'] = 'Bob' # error

Output:

Difference between MappingProxyType and PEP 416 frozendict

MappingProxyType is a read-only proxy for mapping (e.g. dict) objects and frozendict is an immutable dict.

The MappingProxyType is just a simple proxy (i.e. interface) to access the real object (the real map, which in our example is dict).

the suggested frozendict the object is just as the set is to frozenset. a read-only (immutable) object which can only be changed upon creation.

So why do we need MappingProxyType? example use case is where you want to pass a dictionary to another function but without it being able to change your dictionary, it acts as a read-only proxy, (quoting python docs):

Do comment if you have any doubts or suggestions on this Python dictionary topic.

Note: IDE: PyCharm 2021.3.3 (Community Edition)

Windows 10

Python 3.10.1

All Python Examples are in Python 3, so Maybe its different from python 2 or upgraded versions.