Immut

An immutable container library for Python

Use case

The intended use case for this library is to create named immutable container classes to use in an application. This would be particularly useful for value objects. Create an immutable container to hold a bunch of data with named fields and pass it freely around the application knowing that the contents will not be modified after creation.

Example usage

pip install immut

from immut import ImmutableContainer

ResponseModel = ImmutableContainer('ResponseModel', 'message', 'code')
response = ResponseModel(message='success')
response.message  # returns 'success'
response.code  # returns None

# The fields can be anything
u = User('jonathan')
RequestModel = ImmutableContainer('RequestModel', 'user')
request = RequestModel(user=u)

API

The sole API is for creating a container.

ImmutableContainer(container_name, *fields)

Parameters

• container_name the name of the class for the container (string). Generally, simply set it to the name of the variable you are assigning to.
• fields each field is a string representing the fields that this container will have

Returns A dynamically generated immutable container

Behavior

• Trying to set a specified field on the immutable container after creation will raise an AttributeError.
• Setting a non-specified field in the constructor will raise a ValueError
  • Setting a non-specified field on the container after construction is allowed, but is not recommended as it is outside the scope of the use case and is bad python programming practice in general.
• Non-initialized fields in the constructor will return None when accessed.

Disclaimer

I know this isn't the most pythonic or useful library in the world. It was conceived as a way for me to learn how meta classes work. However, it has its uses, and it is well tested.

Differences with collections.namedtuple

There are many similarities with this library and collections.namedtuple. The main difference is in the behavior with initialization. With a namedtuple, each defined attribute must be initialized in the constructor but with this container library, attributes are initialized to None by default if they are unspecified in the constructor.