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==========
frozenlist
==========

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Introduction
============

``frozenlist.FrozenList`` is a list-like structure which implements
``collections.abc.MutableSequence``. The list is *mutable* until ``FrozenList.freeze``
is called, after which list modifications raise ``RuntimeError``:


>>> from frozenlist import FrozenList
>>> fl = FrozenList([17, 42])
>>> fl.append('spam')
>>> fl.append('Vikings')
>>> fl
<FrozenList(frozen=False, [17, 42, 'spam', 'Vikings'])>
>>> fl.freeze()
>>> fl
<FrozenList(frozen=True, [17, 42, 'spam', 'Vikings'])>
>>> fl.frozen
True
>>> fl.append("Monty")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "frozenlist/_frozenlist.pyx", line 97, in frozenlist._frozenlist.FrozenList.append
    self._check_frozen()
  File "frozenlist/_frozenlist.pyx", line 19, in frozenlist._frozenlist.FrozenList._check_frozen
    raise RuntimeError("Cannot modify frozen list.")
RuntimeError: Cannot modify frozen list.


FrozenList is also hashable, but only when frozen. Otherwise it also throws a RuntimeError:


>>> fl = FrozenList([17, 42, 'spam'])
>>> hash(fl)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "frozenlist/_frozenlist.pyx", line 111, in frozenlist._frozenlist.FrozenList.__hash__
    raise RuntimeError("Cannot hash unfrozen list.")
RuntimeError: Cannot hash unfrozen list.
>>> fl.freeze()
>>> hash(fl)
3713081631934410656
>>> dictionary = {fl: 'Vikings'} # frozen fl can be a dict key
>>> dictionary
{<FrozenList(frozen=True, [1, 2])>: 'Vikings'}


Installation
------------

::

   $ pip install frozenlist

The library requires Python 3.6 or newer.


Documentation
=============

https://frozenlist.readthedocs.io/

Communication channels
======================

*aio-libs discourse group*: https://aio-libs.discourse.group

Feel free to post your questions and ideas here.

*gitter chat* https://gitter.im/aio-libs/Lobby

Requirements
============

- Python >= 3.6

License
=======

``frozenlist`` is offered under the Apache 2 license.

Source code
===========

The project is hosted on GitHub_

Please file an issue in the `bug tracker
<https://github.com/aio-libs/frozenlist/issues>`_ if you have found a bug
or have some suggestions to improve the library.

.. _GitHub: https://github.com/aio-libs/frozenlist