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immutables
==========
.. image:: https://github.com/MagicStack/immutables/workflows/Tests/badge.svg?branch=master
:target: https://github.com/MagicStack/immutables/actions?query=workflow%3ATests+branch%3Amaster+event%3Apush
.. image:: https://img.shields.io/pypi/v/immutables.svg
:target: https://pypi.python.org/pypi/immutables
An immutable mapping type for Python.
The underlying datastructure is a Hash Array Mapped Trie (HAMT)
used in Clojure, Scala, Haskell, and other functional languages.
This implementation is used in CPython 3.7 in the ``contextvars``
module (see `PEP 550 <https://www.python.org/dev/peps/pep-0550/>`_ and
`PEP 567 <https://www.python.org/dev/peps/pep-0567/>`_ for more details).
Immutable mappings based on HAMT have O(log N) performance for both
``set()`` and ``get()`` operations, which is essentially O(1) for
relatively small mappings.
Below is a visualization of a simple get/set benchmark comparing
HAMT to an immutable mapping implemented with a Python dict
copy-on-write approach (the benchmark code is available
`here <https://gist.github.com/1st1/292e3f0bbe43bd65ff3256f80aa2637d>`_):
.. image:: bench.png
Installation
------------
``immutables`` requires Python 3.6+ and is available on PyPI::
$ pip install immutables
API
---
``immutables.Map`` is an unordered immutable mapping. ``Map`` objects
are hashable, comparable, and pickleable.
The ``Map`` object implements the ``collections.abc.Mapping`` ABC
so working with it is very similar to working with Python dicts:
.. code-block:: python
import immutables
map = immutables.Map(a=1, b=2)
print(map['a'])
# will print '1'
print(map.get('z', 100))
# will print '100'
print('z' in map)
# will print 'False'
Since Maps are immutable, there is a special API for mutations that
allow apply changes to the Map object and create new (derived) Maps:
.. code-block:: python
map2 = map.set('a', 10)
print(map, map2)
# will print:
# <immutables.Map({'a': 1, 'b': 2})>
# <immutables.Map({'a': 10, 'b': 2})>
map3 = map2.delete('b')
print(map, map2, map3)
# will print:
# <immutables.Map({'a': 1, 'b': 2})>
# <immutables.Map({'a': 10, 'b': 2})>
# <immutables.Map({'a': 10})>
Maps also implement APIs for bulk updates: ``MapMutation`` objects:
.. code-block:: python
map_mutation = map.mutate()
map_mutation['a'] = 100
del map_mutation['b']
map_mutation.set('y', 'y')
map2 = map_mutation.finish()
print(map, map2)
# will print:
# <immutables.Map({'a': 1, 'b': 2})>
# <immutables.Map({'a': 100, 'y': 'y'})>
``MapMutation`` objects are context managers. Here's the above example
rewritten in a more idiomatic way:
.. code-block:: python
with map.mutate() as mm:
mm['a'] = 100
del mm['b']
mm.set('y', 'y')
map2 = mm.finish()
print(map, map2)
# will print:
# <immutables.Map({'a': 1, 'b': 2})>
# <immutables.Map({'a': 100, 'y': 'y'})>
Further development
-------------------
* An immutable version of Python ``set`` type with efficient
``add()`` and ``discard()`` operations.
License
-------
Apache 2.0
|
