18 – Immutable dictionary

18 – Immutable dictionary#

The module types exposes MappingProxyType, a type that’s essentially an immutable dictionary.

So, if you want an immutable dictionary, create a regular one and wrap it in MappingProxyType:

from types import MappingProxyType

my_dict = MappingProxyType(
    {
        "url": "mathspp.com",
        "email": "rodrigo@mathspp.com",
    }
)

print(my_dict["url"])  # mathspp.com

# TypeErrors:
my_dict["name"] = "Rodrigo"
my_dict["url"] = ""

Be careful not to keep references to the underlying dictionary, though… If you do, and if you modify the underlying dictionary, the changes are reflected in the immutable dictionary:

from types import MappingProxyType

base_dict = {
    "url": "mathspp.com",
    "email": "rodrigo@mathspp.com",
}
immutable = MappingProxyType(base_dict)

print(immutable["url"])  # mathspp.com

base_dict["url"] = "example.com"
print(immutable["url"])  # example.com