96 lines
2.4 KiB
Python
96 lines
2.4 KiB
Python
"""Manage shelves of pickled objects.
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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 can
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be essentially arbitrary Python objects -- anything that the "pickle"
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module can handle. This includes most class instances, recursive data
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types, and objects containing lots of shared sub-objects. The keys
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are ordinary strings.
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To summarize the interface (key is a string, data is an arbitrary
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object):
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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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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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"""
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import pickle
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import StringIO
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class Shelf:
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"""Base class for shelf implementations.
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This is initialized with a dictionary-like object.
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See the module's __doc__ string for an overview of the interface.
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"""
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def __init__(self, dict):
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self.dict = dict
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def keys(self):
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return self.dict.keys()
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def __len__(self):
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return self.dict.len()
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def has_key(self, key):
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return self.dict.has_key(key)
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def __getitem__(self, key):
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f = StringIO.StringIO(self.dict[key])
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return pickle.Unpickler(f).load()
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def __setitem__(self, key, value):
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f = StringIO.StringIO()
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p = pickle.Pickler(f)
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p.dump(value)
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self.dict[key] = f.getvalue()
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def __delitem__(self, key):
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del self.dict[key]
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def close(self):
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if hasattr(self.dict, 'close'):
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self.dict.close()
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self.dict = None
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def __del__(self):
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self.close()
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class DbShelf(Shelf):
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"""Shelf implementation using the "anydbm" generic dbm interface.
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This is initialized with the filename for the dbm database.
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See the module's __doc__ string for an overview of the interface.
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"""
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def __init__(self, filename):
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import anydbm
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Shelf.__init__(self, anydbm.open(filename))
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def open(filename):
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"""Open a persistent dictionary for reading and writing.
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Argument is the filename for the dbm database.
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See the module's __doc__ string for an overview of the interface.
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"""
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return DbShelf(filename)
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