accretive 2.0

Accretive data structures.

A Python library package which provides accretive data structures.

Accretive data structures can grow at any time but can never shrink. An accretive dictionary accepts new entries, but cannot have existing entries altered or removed. Similarly, an accretive namespace accepts new attributes, but cannot have existing attributes assigned to new values or deleted.

Accretive data structures are useful as registries, which may be incrementally initialized, but should have immutable state, once initialized. In general, they are a good compromise between the safety of immutability and the convenience of incremental initialization.

Note

Enforcement of immutability is quite difficult in Python. While this library encourages immutability by default, it can be circumvented by anyone who has intermediate knowledge of Python machinery and who is determined to circumvent the immutability. Use the library in the spirit of making programs safer, but understand that it cannot truly prevent unwanted state tampering.

In addition to accretive dictionaries (including dictionaries with default entries) and namespaces, this package also provides accretive classes (including abstract base classes), modules, and objects. Subpackages provide variants of all of these with some additional behaviors or constraints. Modules of aliases are also provided to satisfy various import styles and nomenclatural conventions.

Examples

Accretive Namespace

An accretive namespace, similar to types.SimpleNamespace, is available. This namespace can be initialized from multiple iterables and from keyword arguments. (Keyword arguments shown below; see documentation for additional forms of initialization.)

>>> from accretive import Namespace
>>> ns = Namespace( apples = 12, bananas = 6, cherries = 42 )
>>> ns
accretive.namespaces.Namespace( apples = 12, bananas = 6, cherries = 42 )

Arbitrary attributes can be assigned, as is expected in Python.

>>> ns.blueberries = 96
>>> ns.strawberries = 24
>>> ns
accretive.namespaces.Namespace( apples = 12, bananas = 6, cherries = 42, blueberries = 96, strawberries = 24 )

Since the namespace is accretive, attributes cannot be deleted.

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

Or reassigned.

>>> ns.apples = 14
Traceback (most recent call last):
...
accretive.exceptions.IndelibleAttributeError: Cannot reassign or delete existing attribute 'apples'.

The attributes thus retain their original values.

>>> ns
accretive.namespaces.Namespace( apples = 12, bananas = 6, cherries = 42, blueberries = 96, strawberries = 24 )

Accretive Dictionary

An accretive dictionary, similar to dict, is available. This dictionary can be initialized from multiple iterables and from keyword arguments. (Keyword arguments shown below; see documentation for additional forms of initialization.)

>>> from accretive import Dictionary
>>> dct = Dictionary( apples = 12, bananas = 6, cherries = 42 )
>>> dct
accretive.dictionaries.Dictionary( {'apples': 12, 'bananas': 6, 'cherries': 42} )

Entries can be added to the dictionary after initialization. This includes via a batch operation, such as update, which can accept the same forms of arguments as dictionary initialization.

>>> dct.update( blueberries = 96, strawberries = 24 )
accretive.dictionaries.Dictionary( {'apples': 12, 'bananas': 6, 'cherries': 42, 'blueberries': 96, 'strawberries': 24} )

Since the dictionary is accretive, existing entries cannot be removed.

>>> del dct[ 'bananas' ]
Traceback (most recent call last):
...
accretive.exceptions.IndelibleEntryError: Cannot update or remove existing entry for 'bananas'.

Or altered.

>>> dct[ 'bananas' ] = 11
Traceback (most recent call last):
...
accretive.exceptions.IndelibleEntryError: Cannot update or remove existing entry for 'bananas'.

The entries thus remain unchanged.

>>> dct
accretive.dictionaries.Dictionary( {'apples': 12, 'bananas': 6, 'cherries': 42, 'blueberries': 96, 'strawberries': 24} )

Installation

pip install accretive

More Flair

…than the required minimum