by RaRe-Technologies

RaRe-Technologies /sqlitedict

Persistent dict, backed by sqlite3 and pickle, multithread-safe.

548 Stars 89 Forks Last release: about 2 years ago (1.6.0) Apache License 2.0 211 Commits 7 Releases

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sqlitedict -- persistent
, backed-up by SQLite and pickle

|Travis|_ |License|_

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A lightweight wrapper around Python's sqlite3 database with a simple, Pythonic dict-like interface and support for multi-thread access:

.. code-block:: python

from sqlitedict import SqliteDict mydict = SqliteDict('./mydb.sqlite', autocommit=True) mydict['somekey'] = anypicklableobject 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 mydict.close()

Pickle is used internally to (de)serialize the values. Keys are arbitrary strings, values arbitrary pickle-able objects.

If you don't use autocommit (default is no autocommit for performance), then don't forget to call

when done with a transaction:

.. code-block:: python

using SqliteDict as context manager works too (RECOMMENDED)

with SqliteDict('./mydb.sqlite') as mydict: # note no autocommit=True ... mydict['somekey'] = u"first value" ... mydict['anotherkey'] = range(10) ... mydict.commit() ... mydict['somekey'] = u"new value" ... # no explicit commit here with SqliteDict('./mydb.sqlite') as mydict: # re-open the same DB ... print mydict['somekey'] # outputs 'first value', not 'new value'


  • Values can be any picklable objects (uses
    with the highest protocol).
  • Support for multiple tables (=dicts) living in the same database file.
  • Support for access from multiple threads to the same connection (needed by e.g. Pyro). Vanilla sqlite3 gives you
    ProgrammingError: SQLite objects created in a thread can
    only be used in that same thread.

Concurrent requests are still serialized internally, so this "multithreaded support" doesn't give you any performance benefits. It is a work-around for sqlite limitations in Python.

  • 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)


The module has no dependencies beyond Python itself. The minimum Python version is 2.5, continuously tested on Python 2.6, 2.7, 3.3 and 3.4

on Travis 

Install or upgrade with::

pip install -U sqlitedict

or from the

source tar.gz 
python setup.py install


Standard Python document strings are inside the module:

.. code-block:: python

import sqlitedict help(sqlitedict)

(but it's just

with a commit, really).

Beware: because of Python semantics,

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

.. code-block:: python

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

For developers


# 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

resides on
_. You can file issues or pull requests there.

is open source software released under the
Apache 2.0 license 
. Copyright (c) 2011-now
Radim Řehůřek 
and contributors.

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