11.10. dbhash — DBM-style interface to the BSD database library - Python 2.7.18 documentation 编辑

Deprecated since version 2.6: The dbhash module has been removed in Python 3.

The dbhash module provides a function to open databases using the BSD db library. This module mirrors the interface of the other Python database modules that provide access to DBM-style databases. The bsddb module is required to use dbhash.

This module provides an exception and a function:

exception dbhash.error

Exception raised on database errors other than KeyError. It is a synonym for bsddb.error.

dbhash.open(path[, flag[, mode]])

Open a db database and return the database object. The path argument is the name of the database file.

The flag argument can be:

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

For platforms on which the BSD db library supports locking, an 'l' can be appended to indicate that locking should be used.

The optional mode parameter is used to indicate the Unix permission bits that should be set if a new database must be created; this will be masked by the current umask value for the process.

See also

Module anydbm

Generic interface to dbm-style databases.

Module bsddb

Lower-level interface to the BSD db library.

Module whichdb

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

11.10.1. Database Objects

The database objects returned by open() provide the methods common to all the DBM-style databases and mapping objects. The following methods are available in addition to the standard methods.

dbhash.first()

It’s possible to loop over every key/value pair in the database using this method and the next() method. The traversal is ordered by the databases internal hash values, and won’t be sorted by the key values. This method returns the starting key.

dbhash.last()

Return the last key/value pair in a database traversal. This may be used to begin a reverse-order traversal; see previous().

dbhash.next()

Returns the key next key/value pair in a database traversal. The following code prints every key in the database db, without having to create a list in memory that contains them all:

print db.first()
for i in xrange(1, len(db)):
    print db.next()

dbhash.previous()

Returns the previous key/value pair in a forward-traversal of the database. In conjunction with last(), this may be used to implement a reverse-order traversal.

dbhash.sync()

This method forces any unwritten data to be written to the disk.