![]() ![]() Program has a shelf open for writing, no other program should have it open for (Multiple simultaneous read accesses are safe.) When a The shelve module does not support concurrent read/write access to This means that (the pickled representation of) the objects stored in theĭatabase should be fairly small, and in rare cases key collisions may cause (unfortunately) subject to the limitations of dbm, if it is used. Safe to open the database directly using dbm. The choice of which database package will be used (such as dbm.ndbm orĭbm.gnu) depends on which interface is available. Very slow since all accessed entries are written back (there is no way toĭetermine which accessed entries are mutable, nor which ones were actually Vast amounts of memory for the cache, and it can make the close operation The persistent dictionary, but, if many entries are accessed, it can consume Optional writeback parameter is set to True, all entries accessed are alsoĬached in memory, and written back on sync() andĬlose() this can make it handier to mutate mutable entries in Written only when assigned to the shelf (see Example). The version of the pickle protocol can be specifiedīecause of Python semantics, a shelf cannot know when a mutable Has the same interpretation as the flag parameter of dbm.open().īy default, pickles created with pickle.DEFAULT_PROTOCOL are used By default, the underlyingĭatabase file is opened for reading and writing. As a side-effect, an extension may be added to theįilename and more than one file may be created. The filename specified is the base filename for open ( filename, flag = 'c', protocol = None, writeback = False ) ¶ This includes most class instances, recursive data types, and objects containing ![]() The difference with “dbm”ĭatabases is that the values (not the keys!) in a shelf can be essentiallyĪrbitrary Python objects - anything that the pickle module can handle. A “shelf” is a persistent, dictionary-like object. ![]()
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