"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 있습
   니다 --- "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 주
   어진 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 닫힙
니다.

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 (GNU dbm)
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 지정
   과 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 모
      든 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 기록
      되지 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 (New Database
Manager) library. This module can be used with the "classic" NDBM
interface or the GDBM (GNU dbm) 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 지정
   과 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 않습니
  다.

======================================================================

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 지정
   과 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.
