Class

Accretive classes are similar to standard Python classes, but with the added property that once an attribute is set, it cannot be altered or removed. This makes them useful for defining constants or configurations that should remain immutable once defined.

>>> from accretive import Class

Initialization

Accretive classes can be defined using the Class metaclass. Attributes can be added during class definition.

>>> class Config( metaclass = Class ):
...     host = 'localhost'
...     port = 8080
>>> Config.host
'localhost'

Immutability

Existing attributes cannot be reassigned.

>>> Config.host = '127.0.0.1'
Traceback (most recent call last):
...
accretive.exceptions.IndelibleAttributeError: Cannot reassign or delete existing attribute 'host'.

Or deleted.

>>> del Config.port
Traceback (most recent call last):
...
accretive.exceptions.IndelibleAttributeError: Cannot reassign or delete existing attribute 'port'.

Attribute Assignment

However, new attributes can be assigned.

>>> Config.new_feature = 'enabled'
>>> Config.new_feature
'enabled'

Decorator Usage

Accretive classes can also use decorators to modify class behavior. Decorators can add new attributes, but cannot modify existing ones.

>>> def add_version( cls ):
...     cls.version = '1.0'
...     return cls
>>> class AppConfig( metaclass = Class, decorators = ( add_version, ) ):
...     name = 'MyApp'
>>> AppConfig.version
'1.0'
>>> AppConfig.name
'MyApp'
>>> AppConfig.name = 'NewApp'
Traceback (most recent call last):
...
accretive.exceptions.IndelibleAttributeError: Cannot reassign or delete existing attribute 'name'.

Dynamic Docstring Assignment

Accretive classes support dynamic docstring assignment, allowing for computed docstrings to be set at class creation.

>>> class DocumentedConfig( metaclass = Class, docstring = 'Dynamic docstring' ):
...     ''' Static docstring '''
...     host = 'localhost'
>>> DocumentedConfig.__doc__
'Dynamic docstring'