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Persistent compressed expiring dict in Python, backed up by sqlite3 and pickle, with auto-cleaning and auto-vacuuming semantics

Project description

=========================================================================
expiringsqlitedict -- persistent ``dict``, backed-up by SQLite and pickle
=========================================================================

|License|_

.. _Downloads: https://pypi.python.org/pypi/expiringsqlitedict
.. _License: https://pypi.python.org/pypi/expiringsqlitedict

A lightweight wrapper around Python's sqlite3 database with a simple, Pythonic
dict-like interface. This fork is modified to implement a metatable and
automatic expiring and vacuuming semantics, as well as some appropriate locking.
This also compresses values automatically.

.. code-block:: python

>>> from expiringsqlitedict import SqliteDict
>>> with SqliteDict('./my_db.sqlite', autocommit=True) as mydict:
>>> mydict['some_key'] = any_picklable_object
>>> print mydict['some_key'] # prints the new value
>>> for key, value in mydict.iteritems():
>>> print key, value
>>> print len(mydict) # etc... all dict functions work

Pickle is used internally to (de)serialize the values. Keys are arbitrary strings,
values arbitrary pickle-able objects. This must be used within a context
manager.

Features
--------

* Values can be **any picklable objects** (uses ``cPickle`` with the highest protocol).
* Support for **access from multiple programs or threads**, using a lockfile.
* Support for **custom serialization or compression**:

.. code-block:: python

# use JSON instead of pickle
>>> import json
>>> mydict = SqliteDict('./my_db.sqlite', encode=json.dumps, decode=json.loads)

# apply zlib compression after pickling
>>> import zlib, pickle, sqlite3
>>> def my_encode(obj):
... return sqlite3.Binary(zlib.compress(pickle.dumps(obj, pickle.HIGHEST_PROTOCOL)))
>>> def my_decode(obj):
... return pickle.loads(zlib.decompress(bytes(obj)))
>>> mydict = SqliteDict('./my_db.sqlite', encode=my_encode, decode=my_decode)


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

The module has no dependencies beyond Python itself.

Install or upgrade with::

pip install expiringsqlitedict

or from the `source tar.gz <http://pypi.python.org/pypi/expiringsqlitedict>`_::

python setup.py install

Documentation
-------------

Standard Python document strings are inside the module:

.. code-block:: python

>>> import expiringsqlitedict
>>> help(expiringsqlitedict)

(but it's just ``dict`` with a commit, really).

**Beware**: because of Python semantics, ``expiringsqlitedict`` cannot know when
a mutable SqliteDict-backed entry was modified in RAM. For example,
``mydict.setdefault('new_key', []).append(1)`` will leave ``mydict['new_key']``
equal to empty list, not ``[1]``. You'll need to explicitly assign the mutated
object back to SqliteDict to achieve the same effect:

.. code-block:: python

>>> val = mydict.get('new_key', [])
>>> val.append(1) # sqlite DB not updated here!
>>> mydict['new_key'] = val # now updated


For developers
--------------

Install::

# pip install nose
# pip install coverage

To perform all tests::

# make test-all

To perform all tests with coverage::

# make test-all-with-coverage


Comments, bug reports
---------------------

``expiringsqlitedict`` resides on `github <https://github.com/absperf/expiringsqlitedict>`_. You can file issues or pull
requests there.


----

``expiringsqlitedict`` is open source software released under the
`Apache 2.0 license <http://opensource.org/licenses/apache2.0.php>`_.
Copyright (c) 2011-2018 `Radim Řehůřek <http://radimrehurek.com>`_ and
contributors. The changes in this fork copyright (c) 2018 Absolute Performance,
Inc.


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