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12. Data Compression and Archiving

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11. Data PersistenceΒΆ

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 bsddb module also provides such disk-based string-to-string mappings based on hashing, and also supports B-Tree and record-based formats.

The list of modules described in this chapter is:

  • pickle — Python object serialization * Relationship to other Python modules * Data stream format * Usage * What can be pickled and unpickled? * The pickle protocol

    • Pickling and unpickling normal class instances
    • Pickling and unpickling extension types
    • Pickling and unpickling external objects
    • Subclassing Unpicklers
    • Example
  • cPickle — A faster pickle

  • copy_reg — Register pickle support functions

  • shelve — Python object persistence * Restrictions * Example

  • marshal — Internal Python object serialization

  • anydbm — Generic access to DBM-style databases

  • whichdb — Guess which DBM module created a database

  • dumbdbm — Portable DBM implementation * Dumbdbm Objects