Persistent dict in Python, backed up by sqlite3 and pickle, multithread-safe.
A lightweight wrapper around Python’s sqlite3 database with a simple, Pythonic dict-like interface and support for multi-thread access:
>>> from sqlitedict import SqliteDict >>> mydict = SqliteDict('./my_db.sqlite', autocommit=True) >>> 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 >>> 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 mydict.commit() when done with a transaction:
>>> # using SqliteDict as context manager works too (RECOMMENDED) >>> with SqliteDict('./my_db.sqlite') as mydict: # note no autocommit=True ... mydict['some_key'] = u"first value" ... mydict['another_key'] = range(10) ... mydict.commit() ... mydict['some_key'] = u"new value" ... # no explicit commit here >>> with SqliteDict('./my_db.sqlite') as mydict: # re-open the same DB ... print mydict['some_key'] # outputs 'first value', not 'new value'
Values can be any picklable objects (uses cPickle 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:
# 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:
>>> import sqlitedict >>> help(sqlitedict)
(but it’s just dict with a commit, really).
Beware: because of Python semantics, sqlitedict 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 . You’ll need to explicitly assign the mutated object back to SqliteDict to achieve the same effect:
>>> val = mydict.get('new_key', ) >>> val.append(1) # sqlite DB not updated here! >>> mydict['new_key'] = val # now updated
# pip install nose # pip install coverage
To perform all tests:
# make test-all
To perform all tests with coverage:
# make test-all-with-coverage