12. Data Persistence
********************

The modules described in this chapter support storing Python data in a
persistent form on disk.  The "pickle" and "marshal" modules can turn
many Python data types into a stream of bytes and then recreate the
objects from the bytes.  The various DBM-related modules support a
family of hash-based file formats that store a mapping of strings to
other strings.

The list of modules described in this chapter is:

* 12.1. "pickle" --- Python object serialization

  * 12.1.1. Relationship to other Python modules

    * 12.1.1.1. Comparison with "marshal"

    * 12.1.1.2. Comparison with "json"

  * 12.1.2. Data stream format

  * 12.1.3. Module Interface

  * 12.1.4. What can be pickled and unpickled?

  * 12.1.5. Pickling Class Instances

    * 12.1.5.1. Persistence of External Objects

    * 12.1.5.2. Dispatch Tables

    * 12.1.5.3. Handling Stateful Objects

  * 12.1.6. Restricting Globals

  * 12.1.7. Performance

  * 12.1.8. Examples

* 12.2. "copyreg" --- Register "pickle" support functions

  * 12.2.1. Example

* 12.3. "shelve" --- Python object persistence

  * 12.3.1. Restrictions

  * 12.3.2. Example

* 12.4. "marshal" --- Internal Python object serialization

* 12.5. "dbm" --- Interfaces to Unix "databases"

  * 12.5.1. "dbm.gnu" --- GNU's reinterpretation of dbm

  * 12.5.2. "dbm.ndbm" --- Interface based on ndbm

  * 12.5.3. "dbm.dumb" --- Portable DBM implementation

* 12.6. "sqlite3" --- DB-API 2.0 interface for SQLite databases

  * 12.6.1. Module functions and constants

  * 12.6.2. Connection Objects

  * 12.6.3. Cursor Objects

  * 12.6.4. Row Objects

  * 12.6.5. Exceptions

  * 12.6.6. SQLite and Python types

    * 12.6.6.1. 簡介

    * 12.6.6.2. Using adapters to store additional Python types in
      SQLite databases

      * 12.6.6.2.1. Letting your object adapt itself

      * 12.6.6.2.2. Registering an adapter callable

    * 12.6.6.3. Converting SQLite values to custom Python types

    * 12.6.6.4. Default adapters and converters

  * 12.6.7. Controlling Transactions

  * 12.6.8. Using "sqlite3" efficiently

    * 12.6.8.1. Using shortcut methods

    * 12.6.8.2. Accessing columns by name instead of by index

    * 12.6.8.3. Using the connection as a context manager

  * 12.6.9. Common issues

    * 12.6.9.1. Multithreading
