shelve.py :  » Language-Interface » ChinesePython » chinesepython2.1.3-0.4 » Lib » Python Open Source

Home
Python Open Source
1.3.1.2 Python
2.Ajax
3.Aspect Oriented
4.Blog
5.Build
6.Business Application
7.Chart Report
8.Content Management Systems
9.Cryptographic
10.Database
11.Development
12.Editor
13.Email
14.ERP
15.Game 2D 3D
16.GIS
17.GUI
18.IDE
19.Installer
20.IRC
21.Issue Tracker
22.Language Interface
23.Log
24.Math
25.Media Sound Audio
26.Mobile
27.Network
28.Parser
29.PDF
30.Project Management
31.RSS
32.Search
33.Security
34.Template Engines
35.Test
36.UML
37.USB Serial
38.Web Frameworks
39.Web Server
40.Web Services
41.Web Unit
42.Wiki
43.Windows
44.XML
Python Open Source » Language Interface » ChinesePython 
ChinesePython » chinesepython2.1.3 0.4 » Lib » shelve.py
"""Manage shelves of pickled objects.

A "shelf" is a persistent, dictionary-like object.  The difference
with dbm databases is that the values (not the keys!) in a shelf can
be essentially arbitrary Python objects -- anything that the "pickle"
module can handle.  This includes most class instances, recursive data
types, and objects containing lots of shared sub-objects.  The keys
are ordinary strings.

To summarize the interface (key is a string, data is an arbitrary
object):

        import shelve
        d = shelve.open(filename) # open, with (g)dbm filename -- no suffix

        d[key] = data   # store data at key (overwrites old data if
                        # using an existing key)
        data = d[key]   # retrieve data at key (raise KeyError if no
                        # such key)
        del d[key]      # delete data stored at key (raises KeyError
                        # if no such key)
        flag = d.has_key(key)   # true if the key exists
        list = d.keys() # a list of all existing keys (slow!)

        d.close()       # close it

Dependent on the implementation, closing a persistent dictionary may
or may not be necessary to flush changes to disk.
"""

# Try using cPickle and cStringIO if available.

try:
    from cPickle import Pickler,Unpickler
except ImportError:
    from pickle import Pickler,Unpickler

try:
    from cStringIO import StringIO
except ImportError:
    from StringIO import StringIO

__all__ = ["Shelf","BsdDbShelf","DbfilenameShelf","open"]

class Shelf:
    """Base class for shelf implementations.

    This is initialized with a dictionary-like object.
    See the module's __doc__ string for an overview of the interface.
    """

    def __init__(self, dict):
        self.dict = dict

    def keys(self):
        return self.dict.keys()

    def __len__(self):
        return len(self.dict)

    def has_key(self, key):
        return self.dict.has_key(key)

    def get(self, key, default=None):
        if self.dict.has_key(key):
            return self[key]
        return default

    def __getitem__(self, key):
        f = StringIO(self.dict[key])
        return Unpickler(f).load()

    def __setitem__(self, key, value):
        f = StringIO()
        p = Pickler(f)
        p.dump(value)
        self.dict[key] = f.getvalue()

    def __delitem__(self, key):
        del self.dict[key]

    def close(self):
        try:
            self.dict.close()
        except:
            pass
        self.dict = 0

    def __del__(self):
        self.close()

    def sync(self):
        if hasattr(self.dict, 'sync'):
            self.dict.sync()


class BsdDbShelf(Shelf):
    """Shelf implementation using the "BSD" db interface.

    This adds methods first(), next(), previous(), last() and
    set_location() that have no counterpart in [g]dbm databases.

    The actual database must be opened using one of the "bsddb"
    modules "open" routines (i.e. bsddb.hashopen, bsddb.btopen or
    bsddb.rnopen) and passed to the constructor.

    See the module's __doc__ string for an overview of the interface.
    """

    def __init__(self, dict):
        Shelf.__init__(self, dict)

    def set_location(self, key):
        (key, value) = self.dict.set_location(key)
        f = StringIO(value)
        return (key, Unpickler(f).load())

    def next(self):
        (key, value) = self.dict.next()
        f = StringIO(value)
        return (key, Unpickler(f).load())

    def previous(self):
        (key, value) = self.dict.previous()
        f = StringIO(value)
        return (key, Unpickler(f).load())

    def first(self):
        (key, value) = self.dict.first()
        f = StringIO(value)
        return (key, Unpickler(f).load())

    def last(self):
        (key, value) = self.dict.last()
        f = StringIO(value)
        return (key, Unpickler(f).load())


class DbfilenameShelf(Shelf):
    """Shelf implementation using the "anydbm" generic dbm interface.

    This is initialized with the filename for the dbm database.
    See the module's __doc__ string for an overview of the interface.
    """

    def __init__(self, filename, flag='c'):
        import anydbm
        Shelf.__init__(self, anydbm.open(filename, flag))


def open(filename, flag='c'):
    """Open a persistent dictionary for reading and writing.

    Argument is the filename for the dbm database.
    See the module's __doc__ string for an overview of the interface.
    """

    return DbfilenameShelf(filename, flag)
www.java2java.com | Contact Us
Copyright 2009 - 12 Demo Source and Support. All rights reserved.
All other trademarks are property of their respective owners.