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A list-like structure which implements

Project description

GitHub status for master branch status for master branch frozenlist @ PyPI Read The Docs build status badge Matrix Room — Matrix Space —


frozenlist.FrozenList is a list-like structure which implements 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
>>> 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
  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)
>>> dictionary = {fl: 'Vikings'} # frozen fl can be a dict key
>>> dictionary
{<FrozenList(frozen=True, [1, 2])>: 'Vikings'}


$ pip install frozenlist

The library requires Python 3.8 or newer.


Communication channels

We have a Matrix Space which is also accessible via Gitter.


  • Python >= 3.8


frozenlist is offered under the Apache 2 license.

Source code

The project is hosted on GitHub

Please file an issue in the bug tracker if you have found a bug or have some suggestions to improve the library.

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