MappingProxyType: Creating Read-Only Views of Dictionaries in Python

Hi Pythonistas!

Today, we will learn about MappingProxyType, a powerful tool that allows us to create a read-only yet dynamic view of a dictionary. MappingProxyType provides us with a read-only copy of another dictionary, and interestingly, its values will reflect any changes made to the original dictionary. Let us learn this by an example

Create mappingproxytype

from types import MappingProxyType

original_dict = {'a': 1, 'b': 2, 'c': 3}

read_only_dict = MappingProxyType(original_dict)

Print object

print(read_only_dict)

Output

{'a': 1, 'b': 2, 'c': 3}

Accessing object

print(read_only_dict['a'])

Output

1

Print all keys

print(read_only_dict.keys())

Output

dict_keys(['a', 'b', 'c'])

Print all values

print(read_only_dict.values())

Output

dict_values([1, 2, 3])

Everything on dict works for this objects. But write operation fails

read_only_dict['a']=10

Output

Traceback (most recent call last):

  File "<stdin>", line 1, in <module>

TypeError: 'mappingproxy' object does not support item assignment

Now we can update original dict 

original_dict["d"]=4

print(read_only_dict)

Output

{'a': 1, 'b': 2, 'c': 3, 'd': 4}

We can see that read only dict updated on changing original dict.

When it is useful

We can use this for configuration management, serialization, plugin development etc.

Hope you have learned something new from this post. Please share your valuable suggestions with afsal@parseltongue.co.in