11.6. anydbm — Generic access to DBM-style databases

Note

The anydbm module has been renamed to dbm in Python 3. The 2to3 tool will automatically adapt imports when converting your sources to Python 3.

anydbm is a generic interface to variants of the DBM database — dbhash (requires bsddb), gdbm, or dbm. If none of these modules is installed, the slow-but-simple implementation in module dumbdbm will be used.

anydbm.open(filename[, flag[, mode]])

Open the database file filename and return a corresponding object.

If the database file already exists, the whichdb module is used to determine its type and the appropriate module is used; if it does not exist, the first module listed above that can be imported is used.

The optional flag argument must be one of these values:

Value

Meaning

'r'

Open existing database for reading only (default)

'w'

Open existing database for reading and writing

'c'

Open database for reading and writing, creating it if it doesn’t exist

'n'

Always create a new, empty database, open for reading and writing

If not specified, the default value is 'r'.

The optional mode argument is the Unix mode of the file, used only when the database has to be created. It defaults to octal 0666 (and will be modified by the prevailing umask).

exception anydbm.error

A tuple containing the exceptions that can be raised by each of the supported modules, with a unique exception also named anydbm.error as the first item — the latter is used when anydbm.error is raised.

The object returned by open() supports most of the same functionality as dictionaries; keys and their corresponding values can be stored, retrieved, and deleted, and the has_key() and keys() methods are available. Keys and values must always be strings.

The following example records some hostnames and a corresponding title, and then prints out the contents of the database:

import anydbm

# Open database, creating it if necessary.
db = anydbm.open('cache', 'c')

# Record some values
db['www.python.org'] = 'Python Website'
db['www.cnn.com'] = 'Cable News Network'

# Loop through contents.  Other dictionary methods
# such as .keys(), .values() also work.
for k, v in db.iteritems():
    print k, '\t', v

# Storing a non-string key or value will raise an exception (most
# likely a TypeError).
db['www.yahoo.com'] = 4

# Close when done.
db.close()

In addition to the dictionary-like methods, anydbm objects provide the following method:

anydbm.close()

Close the anydbm database.

See also

Module dbhash

BSD db database interface.

Module dbm

Standard Unix database interface.

Module dumbdbm

Portable implementation of the dbm interface.

Module gdbm

GNU database interface, based on the dbm interface.

Module shelve

General object persistence built on top of the Python dbm interface.

Module whichdb

Utility module used to determine the type of an existing database.