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:

• pickle — Python object serialization
  • Relationship to other Python modules
    • Comparison with marshal
    • Comparison with json
  • Data stream format
  • Module Interface
  • What can be pickled and unpickled?
  • Pickling Class Instances
    • Persistence of External Objects
    • Dispatch Tables
    • Handling Stateful Objects
  • Restricting Globals
  • Performance
  • Examples
• copyreg — Register pickle support functions
  • Example
• shelve — Python object persistence
  • Restrictions
  • Example
• marshal — Internal Python object serialization
• dbm — Interfaces to Unix «databases»
  • dbm.gnu — GNU’s reinterpretation of dbm
  • dbm.ndbm — Interface based on ndbm
  • dbm.dumb — Portable DBM implementation
• sqlite3 — DB-API 2.0 interface for SQLite databases
  • Module functions and constants
  • Connection Objects
  • Cursor Objects
  • Row Objects
  • Exceptions
  • SQLite and Python types
    • Introduction
    • Using adapters to store additional Python types in SQLite databases
      • Letting your object adapt itself
      • Registering an adapter callable
    • Converting SQLite values to custom Python types
    • Default adapters and converters
  • Controlling Transactions
  • Using sqlite3 efficiently
    • Using shortcut methods
    • Accessing columns by name instead of by index
    • Using the connection as a context manager
  • Common issues
    • Multithreading