# `dbm` — Interfaces to Unix “databases”

소스 코드: Lib/dbm/__init__.py

`dbm`은 DBM 데이터베이스 변형에 대한 일반 인터페이스입니다 — `dbm.gnu` 또는 `dbm.ndbm`. 이러한 모듈이 설치되어 있지 않으면, `dbm.dumb` 모듈에 있는 느리지만 간단한 구현이 사용됩니다. 오라클 Berkeley DB에 대한 제삼자 인터페이스가 있습니다.

exception dbm.error

  지원되는 각 모듈에 의해 발생할 수 있는 예외를 포함하는 튜플. 역시 `dbm.error`라고 이름 붙인 고유한 예외를 첫 번째 항목으로 갖고 있습니다 — `dbm.error`가 발생할 때 이것이 사용됩니다.

dbm.whichdb(filename)

  이 함수는 사용 가능한 몇 가지 간단한 데이터베이스 모듈 — `dbm.gnu`, `dbm.ndbm` 또는 `dbm.dumb` — 중 어느 것을 사용하여 주어진 파일을 열어야 하는지 추측합니다.

  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'`

  버전 3.11에서 변경: filename accepts a path-like object.

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

  Open a database and return the corresponding database object.

  매개변수:

    - file (path-like object) –

      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.

  버전 3.11에서 변경: file accepts a path-like object.

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()` methods.

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.

이 객체는 `with` 문에서도 사용되도록 지원해서, 완료될 때 자동으로 닫힙니다.

버전 3.2에서 변경: `get()` and `setdefault()` methods are now available for all `dbm` backends.

버전 3.4에서 변경: Added native support for the context management protocol to the objects returned by `open()`.

버전 3.8에서 변경: Deleting a key from a read-only database raises a database module specific exception instead of `KeyError`.

다음 예제는 일부 호스트 명과 해당 제목을 기록한 다음, 데이터베이스의 내용을 인쇄합니다:

    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.

더 보기

모듈 `shelve`

  문자열이 아닌 데이터를 저장하는 지속성 모듈.

개별 서브 모듈은 다음 섹션에서 설명합니다.

## `dbm.gnu` — GNU database manager

소스 코드: Lib/dbm/gnu.py

The `dbm.gnu` module provides an interface to the GDBM library, similar to the `dbm.ndbm` module, but with additional functionality like crash tolerance.

참고

The file formats created by `dbm.gnu` and `dbm.ndbm` are incompatible and can not be used interchangeably.

exception dbm.gnu.error

  I/O 에러와 같은 `dbm.gnu` 특정 에러에서 발생합니다. 잘못된 키 지정과 같은 일반적인 매핑 에러에 대해서는 `KeyError`가 발생합니다.

dbm.gnu.open(filename, flag='r', mode=0o666, /)

  Open a GDBM database and return a `gdbm` object.

  매개변수:

    - filename (path-like object) – The database file to open.

    - 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.

      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.

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

  예외 발생:

    error – If an invalid flag argument is passed.

  버전 3.11에서 변경: filename accepts a path-like object.

  dbm.gnu.open_flags

    A string of characters the flag parameter of `open()` supports.

  `gdbm` objects behave similar to mappings, but `items()` and `values()` methods are not supported. The following methods are also provided:

  gdbm.firstkey()

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

  gdbm.nextkey(key)

    순회에서 key 뒤에 오는 키를 반환합니다. 다음 코드는 메모리에 모든 키를 포함하는 리스트를 만들지 않고, 데이터베이스 `db`의 모든 키를 인쇄합니다:

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

  gdbm.reorganize()

    If you have carried out a lot of deletions and would like to shrink the space used by the GDBM file, this routine will reorganize the database. `gdbm` objects will not shorten the length of a database file except by using this reorganization; otherwise, deleted file space will be kept and reused as new (key, value) pairs are added.

  gdbm.sync()

    데이터베이스가 빠른 모드로 열렸을 때, 이 메서드를 사용하면 기록되지 않은 데이터가 디스크에 기록됩니다.

  gdbm.close()

    Close the GDBM database.

## `dbm.ndbm` — New Database Manager

소스 코드: Lib/dbm/ndbm.py

The `dbm.ndbm` module provides an interface to the NDBM library. This module can be used with the “classic” NDBM interface or the GDBM compatibility interface.

참고

The file formats created by `dbm.gnu` and `dbm.ndbm` are incompatible and can not be used interchangeably.

경고

The NDBM library shipped as part of macOS has an undocumented limitation on the size of values, which can result in corrupted database files when storing values larger than this limit. Reading such corrupted files can result in a hard crash (segmentation fault).

exception dbm.ndbm.error

  I/O 에러와 같은 `dbm.ndbm` 특정 에러에서 발생합니다. 잘못된 키 지정과 같은 일반적인 매핑 에러에 대해서는 `KeyError`가 발생합니다.

dbm.ndbm.library

  Name of the NDBM implementation library used.

dbm.ndbm.open(filename, flag='r', mode=0o666, /)

  Open an NDBM database and return an `ndbm` object.

  매개변수:

    - filename (path-like object) – The basename of the database file (without the `.dir` or `.pag` extensions).

    - 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.

  `ndbm` objects behave similar to mappings, but `items()` and `values()` methods are not supported. The following methods are also provided:

  버전 3.11에서 변경: Accepts path-like object for filename.

  ndbm.close()

    Close the NDBM database.

## `dbm.dumb` — 이식성 있는 DBM 구현

소스 코드: Lib/dbm/dumb.py

참고

`dbm.dumb` 모듈은 더욱 강인한 모듈을 사용할 수 없을 때 `dbm` 모듈에 대한 최후의 대체 폴백으로 사용됩니다. `dbm.dumb` 모듈은 속도를 위해 작성되지 않았으며 다른 데이터베이스 모듈만큼 많이 사용되지는 않습니다.

The `dbm.dumb` module provides a persistent `dict`-like interface which is written entirely in Python. Unlike other `dbm` backends, such as `dbm.gnu`, no external library is required.

The `dbm.dumb` module defines the following:

exception dbm.dumb.error

  I/O 에러와 같은 `dbm.dumb` 특정 에러에서 발생합니다. 잘못된 키 지정과 같은 일반적인 매핑 에러에 대해서는 `KeyError`가 발생합니다.

dbm.dumb.open(filename, flag='c', mode=0o666)

  Open a `dbm.dumb` database. The returned database object behaves similar to a mapping, in addition to providing `sync()` and `close()` methods.

  매개변수:

    - filename –

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

      - `filename.dat`

      - `filename.dir`

    - flag (str) –

      - `'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.

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

  경고

  파이썬 AST 컴파일러의 스택 깊이 제한으로 인해, 충분히 큰/복잡한 항목이 있는 데이터베이스를 로드할 때 파이썬 인터프리터가 충돌할 수 있습니다.

  버전 3.5에서 변경: `open()` always creates a new database when flag is `'n'`.

  버전 3.8에서 변경: A database opened read-only if flag is `'r'`. A database is not created if it does not exist if flag is `'r'` or `'w'`.

  버전 3.11에서 변경: filename accepts a path-like object.

  In addition to the methods provided by the `collections.abc.MutableMapping` class, the following methods are provided:

  dumbdbm.sync()

    Synchronize the on-disk directory and data files. This method is called by the `shelve.Shelf.sync()` method.

  dumbdbm.close()

    Close the database.