`!dbm` --- Interfaces to Unix "databases"

whichdb(filename)

This function attempts to guess which of the several simple database modules available --- dbm.sqlite3, dbm.gnu, dbm.ndbm, or dbm.dumb --- should be used to open a given file.

Return one of the following values:

• None if the file can't be opened because it's unreadable or doesn't exist
• the empty string ('') if the file's format can't be guessed
• a string containing the required module name, such as 'dbm.ndbm' or 'dbm.gnu'

open(file, flag='r', mode=0o666)

Open a database and return the corresponding database object.

param file
The database file to open.

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

type file
path-like object

param str flag

• 'r' (default): Open existing database for reading only.
• '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.

param int mode
The Unix file access mode of the file (default: octal 0o666), used only when the database has to be created.

open(filename, /, flag="r", mode=0o666)

Open an SQLite database.

param filename
The path to the database to be opened.

type filename
path-like object

param str flag

• 'r' (default): Open existing database for reading only.
• '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.

param mode
The Unix file access mode of the file (default: octal 0o666), used only when the database has to be created.

The returned database object behaves similar to a mutable mapping, but the !keys method returns a list, and the !setdefault method requires two arguments. It also supports a "closing" context manager via the with keyword.

The following methods are also provided:

open(filename, flag="r", mode=0o666, /)

Open a GDBM database and return a !gdbm object.

param filename
The database file to open.

type filename
path-like object

param str flag

• 'r' (default): Open existing database for reading only.
• '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 following additional characters may be appended to control how the database is opened:

• 'f': Open the database in fast mode. Writes to the database will not be synchronized.
• 's': Synchronized mode. Changes to the database will be written immediately to the file.
• 'u': Do not lock database.

Not all flags are valid for all versions of GDBM. See the open_flags member for a list of supported flag characters.

param int mode
The Unix file access mode of the file (default: octal 0o666), used only when the database has to be created.

raises error
If an invalid flag argument is passed.

!gdbm objects behave similar to mutable mappings <mapping>, but methods !items, !values, !pop, !popitem, and !update are not supported, the !keys method returns a list, and the !setdefault method requires two arguments. It also supports a "closing" context manager via the with keyword.

The following methods are also provided:

k = db.firstkey()
while k is not None:
    print(k)
    k = db.nextkey(k)

open(filename, flag="r", mode=0o666, /)

Open an NDBM database and return an !ndbm object.

param filename
The basename of the database file (without the .dir or .pag extensions).

type filename
path-like object

param str flag

• 'r' (default): Open existing database for reading only.
• '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.

param int mode
The Unix file access mode of the file (default: octal 0o666), used only when the database has to be created.

!ndbm objects behave similar to mutable mappings <mapping>, but methods !items, !values, !pop, !popitem, and !update are not supported, the !keys method returns a list, and the !setdefault method requires two arguments. It also supports a "closing" context manager via the with keyword.

The following method is also provided:

open(filename, flag="c", mode=0o666)

Open a !dbm.dumb database.

param filename
The basename of the database file (without extensions). A new database creates the following files:

• {filename}.dat
• {filename}.dir

type database
path-like object

param str flag

• 'r': Open existing database for reading only.
• 'w': Open existing database for reading and writing.
• 'c' (default): 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.

param int mode
The Unix file access mode of the file (default: octal 0o666), used only when the database has to be created.

[!WARNING] It is possible to crash the Python interpreter when loading a database with a sufficiently large/complex entry due to stack depth limitations in Python's AST compiler.

[!WARNING] !dbm.dumb does not support concurrent read/write access. (Multiple simultaneous read accesses are safe.) When a program has the database open for writing, no other program should have it open for reading or writing.

The returned database object behaves similar to a mutable mapping, but the !keys and !items methods return lists, and the !setdefault method requires two arguments. It also supports a "closing" context manager via the with keyword.

The following methods are also provided: