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170 lines
5 KiB
Python
170 lines
5 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; same as "key in d"
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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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# Try using cPickle and cStringIO if available.
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try:
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from cPickle import Pickler, Unpickler
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except ImportError:
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from pickle import Pickler, Unpickler
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try:
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from cStringIO import StringIO
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except ImportError:
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from StringIO import StringIO
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import UserDict
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__all__ = ["Shelf","BsdDbShelf","DbfilenameShelf","open"]
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class Shelf(UserDict.DictMixin):
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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, binary=False):
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self.dict = dict
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self._binary = binary
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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 len(self.dict)
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def has_key(self, key):
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return self.dict.has_key(key)
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def __contains__(self, key):
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return self.dict.has_key(key)
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def get(self, key, default=None):
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if self.dict.has_key(key):
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return self[key]
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return default
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def __getitem__(self, key):
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f = StringIO(self.dict[key])
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return Unpickler(f).load()
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def __setitem__(self, key, value):
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f = StringIO()
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p = Pickler(f, self._binary)
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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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try:
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self.dict.close()
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except:
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pass
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self.dict = 0
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def __del__(self):
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self.close()
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def sync(self):
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if hasattr(self.dict, 'sync'):
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self.dict.sync()
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class BsdDbShelf(Shelf):
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"""Shelf implementation using the "BSD" db interface.
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This adds methods first(), next(), previous(), last() and
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set_location() that have no counterpart in [g]dbm databases.
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The actual database must be opened using one of the "bsddb"
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modules "open" routines (i.e. bsddb.hashopen, bsddb.btopen or
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bsddb.rnopen) and passed to the constructor.
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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, binary=False):
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Shelf.__init__(self, dict, binary)
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def set_location(self, key):
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(key, value) = self.dict.set_location(key)
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f = StringIO(value)
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return (key, Unpickler(f).load())
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def next(self):
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(key, value) = self.dict.next()
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f = StringIO(value)
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return (key, Unpickler(f).load())
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def previous(self):
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(key, value) = self.dict.previous()
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f = StringIO(value)
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return (key, Unpickler(f).load())
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def first(self):
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(key, value) = self.dict.first()
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f = StringIO(value)
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return (key, Unpickler(f).load())
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def last(self):
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(key, value) = self.dict.last()
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f = StringIO(value)
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return (key, Unpickler(f).load())
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class DbfilenameShelf(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, flag='c', binary=False):
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import anydbm
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Shelf.__init__(self, anydbm.open(filename, flag), binary)
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def open(filename, flag='c', binary=False):
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"""Open a persistent dictionary for reading and writing.
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The filename parameter is the base filename for the underlying database.
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As a side-effect, an extension may be added to the filename and more
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than one file may be created. The optional flag parameter has the
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same interpretation as the flag parameter of anydbm.open(). The
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optional binary parameter may be set to True to force the use of binary
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pickles for serializing data values.
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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 DbfilenameShelf(filename, flag, binary)
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