dbm
— Unix 数据库接口
¶
源代码：
Lib/dbm/__init__.py
dbm
is a generic interface to variants of the DBM database:
If none of these modules are installed, the slow-but-simple implementation in module
dbm.dumb
will be used. There is a
third party interface
to the Oracle Berkeley DB.
-
exception
dbm.
error
¶
-
A tuple containing the exceptions that can be raised by each of the supported modules, with a unique exception also named
dbm.error
as the first item — the latter is used when
dbm.error
被引发。
-
dbm.
whichdb
(
filename
)
¶
-
This function attempts to guess which of the several simple database modules available —
dbm.sqlite3
,
dbm.gnu
,
dbm.ndbm
，或
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'
3.11 版改变：
filename
accepts a
像路径对象
.
-
dbm.
open
(
file
,
flag
=
'r'
,
mode
=
0o666
)
¶
-
Open a database and return the corresponding database object.
-
参数
:
-
-
file
(
像路径对象
) –
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.
-
flag
(
str
) –
-
'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.
-
mode
(
int
) – The Unix file access mode of the file (default: octal
0o666
), used only when the database has to be created.
3.11 版改变：
file
accepts a
像路径对象
.
The object returned by
open()
supports the same basic functionality as a
dict
; keys and their corresponding values can be stored, retrieved, and deleted, and the
in
operator and the
keys()
method are available, as well as
get()
and
setdefault()
方法。
Key and values are always stored as
bytes
. This means that when strings are used they are implicitly converted to the default encoding before being stored.
These objects also support being used in a
with
statement, which will automatically close them when done.
3.2 版改变：
get()
and
setdefault()
methods are now available for all
dbm
backends.
3.4 版改变：
Added native support for the context management protocol to the objects returned by
open()
.
3.8 版改变：
Deleting a key from a read-only database raises a database module specific exception instead of
KeyError
.
The following example records some hostnames and a corresponding title, and then prints out the contents of the database:
import dbm
# Open database, creating it if necessary.
with dbm.open('cache', 'c') as db:
# Record some values
db[b'hello'] = b'there'
db['www.python.org'] = 'Python Website'
db['www.cnn.com'] = 'Cable News Network'
# Note that the keys are considered bytes now.
assert db[b'www.python.org'] == b'Python Website'
# Notice how the value is now in bytes.
assert db['www.cnn.com'] == b'Cable News Network'
# Often-used methods of the dict interface work too.
print(db.get('python.org', b'not present'))
# Storing a non-string key or value will raise an exception (most
# likely a TypeError).
db['www.yahoo.com'] = 4
# db is automatically closed when leaving the with statement.
