11.8. dbm — Simple “database” interface - Python 2.7.18 documentation 编辑

Note

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

The dbm module provides an interface to the Unix “(n)dbm” library. Dbm objects behave like mappings (dictionaries), except that keys and values are always strings. Printing a dbm object doesn’t print the keys and values, and the items() and values() methods are not supported.

This module can be used with the “classic” ndbm interface, the BSD DB compatibility interface, or the GNU GDBM compatibility interface. On Unix, the configure script will attempt to locate the appropriate header file to simplify building this module.

The module defines the following:

exception dbm.error: Raised on dbm-specific errors, such as I/O errors. KeyError is raised for general mapping errors like specifying an incorrect key.

dbm.library: Name of the ndbm implementation library used.

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

Open a dbm database and return a dbm object. The filename argument is the name of the database file (without the .dir or .pag extensions; note that the BSD DB implementation of the interface will append the extension .db and only create one file).

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

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).

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