anydbm – Access to DBM-style databases

Purpose:anydbm provides a generic dictionary-like interface to DBM-style, string-keyed databases
Available In:1.4 and later

anydbm is a front-end for DBM-style databases that use simple string values as keys to access records containing strings. It uses the whichdb module to identify dbhash, gdbm, and dbm databases, then opens them with the appropriate module. It is used as a backend for shelve, which knows how to store objects using pickle.

Creating a New Database

The storage format for new databases is selected by looking for each of these modules in order:

The open() function takes flags to control how the database file is managed. To create a new database when necessary, use 'c'. To always create a new database, use 'n'.

import anydbm

db = anydbm.open('/tmp/example.db', 'n')
db['key'] = 'value'
db['today'] = 'Sunday'
db['author'] = 'Doug'
db.close()
$ python anydbm_new.py

In this example, the file is always re-initialized. To see what type of database was created, we can use whichdb.

import whichdb

print whichdb.whichdb('/tmp/example.db')

Your results may vary, depending on what modules are installed on your system.

$ python anydbm_whichdb.py

dbhash

Opening an Existing Database

To open an existing database, use flags of either 'r' (for read-only) or 'w' (for read-write). You don’t need to worry about the format, because existing databases are automatically given to whichdb to identify. If a file can be identified, the appropriate module is used to open it.

import anydbm

db = anydbm.open('/tmp/example.db', 'r')
try:
    print 'keys():', db.keys()
    for k, v in db.iteritems():
        print 'iterating:', k, v
    print 'db["author"] =', db['author']
finally:
    db.close()

Once open, db is a dictionary-like object, with support for the usual methods:

$ python anydbm_existing.py

keys(): ['author', 'key', 'today']
iterating: author Doug
iterating: key value
iterating: today Sunday
db["author"] = Doug

Error Cases

The keys of the database need to be strings.

import anydbm

db = anydbm.open('/tmp/example.db', 'w')
try:
    db[1] = 'one'
except TypeError, err:
    print '%s: %s' % (err.__class__.__name__, err)
finally:
    db.close()

Passing another type results in a TypeError.

$ python anydbm_intkeys.py

TypeError: Integer keys only allowed for Recno and Queue DB's

Values must be strings or None.

import anydbm

db = anydbm.open('/tmp/example.db', 'w')
try:
    db['one'] = 1
except TypeError, err:
    print '%s: %s' % (err.__class__.__name__, err)
finally:
    db.close()

A similar TypeError is raised if a value is not a string.

$ python anydbm_intvalue.py

TypeError: Data values must be of type string or None.

See also

Module shelve
Examples for the shelve module, which uses anydbm to store data.
anydbm
The standard library documentation for this module.
Data Persistence and Exchange
Descriptions of other modules for storing data.
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