Python Disk Collections

Module contains class with extended python list that stores items at disk. By default items before save are pickled and compressed. Use that list as usual list!

In addition, there is implemented extended python deque with disk storage and same behaviour as collections.deque.

Intend of package was to create generic iterables that stores really big collection of items that does not fit in memory and to avoid usage of external cache and local database storages.

>>> from diskcollections.iterables import FileList
>>> flist = FileList()
>>> flist.extend([1, 2, 3])
>>> flist.append(4)
>>> flist
[1, 2, 3, 4]
>>> flist[2]
3
>>> flist2 = flist[:]  # copy makes new FileList
>>> my_list = list(flist)  # now its simple list

>>> from diskcollections.iterables import FileDeque
>>> fdeque = FileDeque()
>>> fdeque.extend([1, 2, 3])
>>> fdeque.append(4)
>>> fdeque
FileDeque([1, 2, 3, 4])
>>> fdeque.pop()
4
>>> fdeque.appendleft(0)
>>> fdeque.popleft()
0

There are available more ways to serialize items.

>>> from diskcollections.iterables import List, FileList, FileDeque
>>> from diskcollections.serializers import (
    PickleSerializer,  # pickle items
    PickleZLibSerializer,  # pickle + compress items
    JsonSerializer, # convert to json items
    JsonZLibSerializer  # convert to json + compress items
)
>>> from functools import partial
>>> JsonFileList = partial(List, serializer_class=JsonHandler)
>>> flist = JsonFileList()
>>> flist.append({'a': 1, 'b': 2, 'c': 3})
>>> flist[0]
{u'a': 1, u'b': 2, u'c': 3}

Installation

To install package type

$ pip install python-disk-collections

How it works

Explaining example above:

>>> from diskcollections.iterables import FileList
>>> from diskcollections.serializers import JsonZLibSerializer
>>>
>>> flist = FileList(serializer_class=JsonZLibSerializer)

New instance of this object creates new temporary directory. By using serializer_class=JsonZLibSerializer each incoming item to list will be: json.dumped and compressed

>>> flist.append({'a': 1, 'b': 2, 'c': 3})

so using this serializer have in mind that all objects you put into list have to lend themself and compatible with json. Exactly this object {'a': 1, 'b': 2, 'c': 3} will serialized and compressed and saved inside temporary directory.

>>> flist[0]
{u'a': 1, u'b': 2, u'c': 3}

Getting an item will read a file and because JsonZLibSerializer is used: then content will be decompressed and tried to loaded from json.

This package provides a few other serializers:

• PickleSerializer - pickle items
• PickleZLibSerializer - pickle + compress items
• JsonSerializer - convert to json items
• JsonZLibSerializer - convert to json + compress items

from diskcollections.serializers import (
      PickleSerializer,
      PickleZLibSerializer,
      JsonSerializer,
      JsonZLibSerializer,
  )

In order to implement your serializer create class with methods: dumps and loads or import interface.

>>> from diskcollections.interfaces import ISerializer

class ISerializer:

@staticmethod
def dumps(obj):
    """Converts object to string.

    :param obj: any python object
    :return: dumped string
    """
    raise NotImplementedError

@staticmethod
def loads(obj):
    """Restored dumped string into python object.

    :param obj: Object stored as string
    :return: python object restored from dump
    """
    raise NotImplementedError

All serializers from example above implements interface ISerializer.

Under the hood, FileList for storage items uses tempfile.mktemp (in python2) or tempfile.TemporaryDirectory (in python3). It means, that every list has own unique directory, placed likely in /tmp/. When list is removed by garbage collector, all items that was stored are lost.

For FileDeque stores items in the same way as FileList.

By default on exit program, or when list or deque is removed: all content of files also are dropped.

To prevent this use PersistentDirectoryClient:

>>> from functools import partial

>>> from diskcollections.iterables import List, PersistentDirectoryClient
>>> from diskcollections.serializers import JsonSerializer
>>> from diskcollections.iterables import PersistentDirectoryClient

>>> dir_abc = partial(PersistentDirectoryClient, "abc")
>>> persistent_list = List(client_class=dir_abc, serializer_class=JsonSerializer)
>>> persistent_list.append({"a": 1, "b": 2})
>>> assert len(persistent_list) == 1
>>> assert open("abc/0").read() == '{"a": 1, "b": 2}'

On exit directory abc with file 0 of his contents will still exist.

Contribute

1. Fork repository on GitHub to start making your changes to the master branch (or branch off of it).
2. Write tests that prove that bug or future works as expected
3. Install other python versions with uv together with tox:

$ pip install uv
$ uv sync
$ uv tool install tox --with tox-uv

1. Install python versions

$ uv python install 3.8 3.9 3.10 3.11 3.12 3.13

1. Check your code and tests with tox

$ tox
---------- coverage: platform linux, python 3.13.2-final-0 -----------
Name                                     Stmts   Miss Branch BrPart  Cover   Missing
------------------------------------------------------------------------------------
diskcollections/__init__.py                  0      0      0      0   100%
diskcollections/iterables/__init__.py        7      0      0      0   100%
diskcollections/iterables/clients.py       112      1     28      1    99%   90
diskcollections/iterables/iterables.py     159      0     74      0   100%
diskcollections/serializers.py              32      0      0      0   100%
------------------------------------------------------------------------------------
TOTAL                                      310      1    102      1    99%

Required test coverage of 95% reached. Total coverage: 99.51%
====================================================================================================== 63 passed, 1 warning in 0.46s =======================================================================================================
  lint: OK (0.55=setup[0.03]+cmd[0.20,0.32] seconds)
  py37: OK (0.47=setup[0.01]+cmd[0.46] seconds)
  py38: OK (0.47=setup[0.01]+cmd[0.46] seconds)
  py39: OK (0.47=setup[0.01]+cmd[0.46] seconds)
  py310: OK (0.63=setup[0.01]+cmd[0.62] seconds)
  py311: OK (0.45=setup[0.01]+cmd[0.45] seconds)
  py312: OK (0.69=setup[0.01]+cmd[0.69] seconds)
  py313: OK (0.75=setup[0.01]+cmd[0.74] seconds)
  evaluation failed :( (4.12 seconds)

1. Lint your code

$ tox -e lint

1. Send a pull request!

License

Python-Disk-Collection is under MIT license, see LICENSE for more details.