klepto: persistent caching to memory, disk, or database

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About Klepto

Klepto extends python's 'lru_cache' to utilize different keymaps and alternate caching algorithms, such as 'lfu_cache' and 'mru_cache'. While caching is meant for fast access to saved results, klepto also has archiving capabilities, for longer-term storage. Klepto uses a simple dictionary-sytle interface for all caches and archives, and all caches can be applied to any python function as a decorator. Keymaps are algorithms for converting a function's input signature to a unique dictionary, where the function's results are the dictionary value. Thus for y = f(x), y will be stored in cache[x] (e.g. {x:y}).

Klepto provides both standard and 'safe' caching, where safe caches are slower but can recover from hashing errors. Klepto is intended to be used for distributed and parallel computing, where several of the keymaps serialize the stored objects. Caches and archives are intended to be read/write accessible from different threads and processes. Klepto enables a user to decorate a function, save the results to a file or database archive, close the interpreter, start a new session, and reload the function and it's cache.

Klepto is part of pathos, a python framework for heterogenous computing. Klepto is in the early development stages, and any user feedback is highly appreciated. Contact Mike McKerns [mmckerns at caltech dot edu] with comments, suggestions, and any bugs you may find. A list of known issues is maintained at

Major Features

Klepto has standard and 'safe' variants of the following::

  • 'lfu_cache' - the least-frequently-used caching algorithm
  • 'lru_cache' - the least-recently-used caching algorithm
  • 'mru_cache' - the most-recently-used caching algorithm
  • 'rr_cache' - the random-replacement caching algorithm
  • 'no_cache' - a dummy caching interface to archiving
  • 'inf_cache' - an infinitely-growing cache

Klepto has the following archive types::

  • 'file_archive' - a dictionary-style interface to a file
  • 'dir_archive' - a dictionary-style interface to a folder of files
  • 'sqltable_archive' - a dictionary-style interface to a sql database table
  • 'sql_archive' - a dictionary-style interface to a sql database
  • 'dict_archive' - a dictionary with an archive interface
  • 'null_archive' - a dictionary-style interface to a dummy archive

Klepto provides the following keymaps::

  • 'keymap' - keys are raw python objects
  • 'hashmap' - keys are a hash for the python object
  • 'stringmap' - keys are the python object cast as a string
  • 'picklemap' - keys are the serialized python object

Klepto also includes a few useful decorators providing::

  • simple, shallow, or deep rounding
  • cryptographic key generation, with masking of selected arguments

Current Release

The latest stable version is klepto-0.1.1. You can download it here.
The latest released version of klepto is always available from::

Klepto is distributed under a 3-clause BSD license.

Development Release

You can get the latest development release with all the shiny new features at::

or even better, fork us on our github mirror of the svn trunk::


If you use klepto to do research that leads to publication, we ask that you
acknowledge use of klepto by citing the following in your publication::

    Michael McKerns and Michael Aivazis,
    "pathos: a framework for heterogeneous computing", 2010- ;

More Information

Probably the best way to get started is to look at the tests that are provide within klepto. See klepto.tests for a set of scripts that test klepto's ability to provide caching and archiving. Klepto's source code is also generally well documented, so further questions may be resolved by inspecting the code itself, or through browsing the  reference manual. For those who like to leap before they look, you can jump right to the installation instructions. If the aforementioned documents do not adequately address your needs, please send us feedback.

Klepto is an active research tool. There are a growing number of publications and presentations that discuss real-world examples and new features of klepto in greater detail than presented in the user's guide. If you would like to share how you use klepto in your work, please send us a link.