mirror of https://github.com/python/cpython.git
39 lines
1.3 KiB
TeX
39 lines
1.3 KiB
TeX
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\section{Built-in module \sectcode{shelve}}
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\stmodindex{shelve}
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\stmodindex{pickle}
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\bimodindex{dbm}
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A ``shelf'' is a persistent, dictionary-like object. The difference
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with ``dbm'' databases is that the values (not the keys!) in a shelf
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can be essentially arbitrary Python objects --- anything that the
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\code{pickle} module can handle. This includes most class instances,
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recursive data types, and objects containing lots of shared
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sub-objects. The keys are ordinary strings.
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To summarize the interface (\code{key} is a string, \code{data} is an
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arbitrary object):
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\begin{verbatim}
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import shelve
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d = shelve.open(filename) # open, with (g)dbm filename -- no suffix
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d[key] = data # store data at key (overwrites old data if
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# using an existing key)
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data = d[key] # retrieve data at key (raise KeyError if no
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# such key)
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del d[key] # delete data stored at key (raises KeyError
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# if no such key)
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flag = d.has_key(key) # true if the key exists
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list = d.keys() # a list of all existing keys (slow!)
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d.close() # close it
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\end{verbatim}
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Dependent on the implementation, closing a persistent dictionary may
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or may not be necessary to flush changes to disk.
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Note: \code{shelve} does not support {\em concurrent} access to
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shelved objects. Two programs should not try to simultaneously access
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the same shelf.
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