Gecko [ v99win.today ]

Name	Size	Permission
2to3.html	63.71 KB	-rw-r--r--
__builtin__.html	11.79 KB	-rw-r--r--
__future__.html	15.58 KB	-rw-r--r--
__main__.html	8.33 KB	-rw-r--r--
_winreg.html	73.99 KB	-rw-r--r--
abc.html	26.82 KB	-rw-r--r--
aepack.html	15.47 KB	-rw-r--r--
aetools.html	18.79 KB	-rw-r--r--
aetypes.html	27.08 KB	-rw-r--r--
aifc.html	29.59 KB	-rw-r--r--
al.html	22.13 KB	-rw-r--r--
allos.html	35.48 KB	-rw-r--r--
anydbm.html	19.31 KB	-rw-r--r--
archiving.html	10.64 KB	-rw-r--r--
argparse.html	269.59 KB	-rw-r--r--
array.html	35.35 KB	-rw-r--r--
ast.html	42.42 KB	-rw-r--r--
asynchat.html	35.84 KB	-rw-r--r--
asyncore.html	43.22 KB	-rw-r--r--
atexit.html	19.23 KB	-rw-r--r--
audioop.html	41.32 KB	-rw-r--r--
autogil.html	9.77 KB	-rw-r--r--
base64.html	24.8 KB	-rw-r--r--
basehttpserver.html	40.6 KB	-rw-r--r--
bastion.html	13.02 KB	-rw-r--r--
bdb.html	50.06 KB	-rw-r--r--
binascii.html	26.64 KB	-rw-r--r--
binhex.html	12.66 KB	-rw-r--r--
bisect.html	28.52 KB	-rw-r--r--
bsddb.html	32.02 KB	-rw-r--r--
bz2.html	31.92 KB	-rw-r--r--
calendar.html	50.16 KB	-rw-r--r--
carbon.html	54.14 KB	-rw-r--r--
cd.html	35.24 KB	-rw-r--r--
cgi.html	58.4 KB	-rw-r--r--
cgihttpserver.html	15.12 KB	-rw-r--r--
cgitb.html	13.5 KB	-rw-r--r--
chunk.html	17.41 KB	-rw-r--r--
cmath.html	32.41 KB	-rw-r--r--
cmd.html	32.69 KB	-rw-r--r--
code.html	28.92 KB	-rw-r--r--
codecs.html	125.92 KB	-rw-r--r--
codeop.html	16.42 KB	-rw-r--r--
collections.html	150.36 KB	-rw-r--r--
colorpicker.html	9.02 KB	-rw-r--r--
colorsys.html	14.38 KB	-rw-r--r--
commands.html	16.63 KB	-rw-r--r--
compileall.html	21.18 KB	-rw-r--r--
compiler.html	78.14 KB	-rw-r--r--
configparser.html	73.92 KB	-rw-r--r--
constants.html	14.68 KB	-rw-r--r--
contextlib.html	22.91 KB	-rw-r--r--
cookie.html	45.38 KB	-rw-r--r--
cookielib.html	102.78 KB	-rw-r--r--
copy.html	14.21 KB	-rw-r--r--
copy_reg.html	15.82 KB	-rw-r--r--
crypt.html	11.62 KB	-rw-r--r--
crypto.html	8.35 KB	-rw-r--r--
csv.html	82.79 KB	-rw-r--r--
ctypes.html	280.57 KB	-rw-r--r--
curses.ascii.html	28.97 KB	-rw-r--r--
curses.html	200.94 KB	-rw-r--r--
curses.panel.html	18.43 KB	-rw-r--r--
custominterp.html	8.59 KB	-rw-r--r--
datatypes.html	18.84 KB	-rw-r--r--
datetime.html	261.02 KB	-rw-r--r--
dbhash.html	18.4 KB	-rw-r--r--
dbm.html	14.75 KB	-rw-r--r--
debug.html	11.28 KB	-rw-r--r--
decimal.html	239.14 KB	-rw-r--r--
development.html	15.27 KB	-rw-r--r--
difflib.html	96.93 KB	-rw-r--r--
dircache.html	13.66 KB	-rw-r--r--
dis.html	96.52 KB	-rw-r--r--
distribution.html	8.27 KB	-rw-r--r--
distutils.html	10.97 KB	-rw-r--r--
dl.html	19.27 KB	-rw-r--r--
doctest.html	193.18 KB	-rw-r--r--
docxmlrpcserver.html	20.02 KB	-rw-r--r--
dumbdbm.html	16.74 KB	-rw-r--r--
dummy_thread.html	11.04 KB	-rw-r--r--
dummy_threading.html	9.96 KB	-rw-r--r--
easydialogs.html	38.83 KB	-rw-r--r--
email-examples.html	47.2 KB	-rw-r--r--
email.charset.html	32.45 KB	-rw-r--r--
email.encoders.html	14.09 KB	-rw-r--r--
email.errors.html	19.2 KB	-rw-r--r--
email.generator.html	24.78 KB	-rw-r--r--
email.header.html	31.12 KB	-rw-r--r--
email.html	55.3 KB	-rw-r--r--
email.iterators.html	14.22 KB	-rw-r--r--
email.message.html	74.91 KB	-rw-r--r--
email.mime.html	34.51 KB	-rw-r--r--
email.parser.html	37.09 KB	-rw-r--r--
email.utils.html	30.04 KB	-rw-r--r--
ensurepip.html	20.21 KB	-rw-r--r--
errno.html	52.31 KB	-rw-r--r--
exceptions.html	73.4 KB	-rw-r--r--
fcntl.html	27.85 KB	-rw-r--r--
filecmp.html	26.49 KB	-rw-r--r--
fileformats.html	10.21 KB	-rw-r--r--
fileinput.html	29.36 KB	-rw-r--r--
filesys.html	11.55 KB	-rw-r--r--
fl.html	71.58 KB	-rw-r--r--
fm.html	15 KB	-rw-r--r--
fnmatch.html	17.78 KB	-rw-r--r--
formatter.html	43.91 KB	-rw-r--r--
fpectl.html	17.84 KB	-rw-r--r--
fpformat.html	12.65 KB	-rw-r--r--
fractions.html	27.17 KB	-rw-r--r--
framework.html	44.24 KB	-rw-r--r--
frameworks.html	8.11 KB	-rw-r--r--
ftplib.html	56.56 KB	-rw-r--r--
functions.html	216.84 KB	-rw-r--r--
functools.html	31.06 KB	-rw-r--r--
future_builtins.html	15.9 KB	-rw-r--r--
gc.html	30.74 KB	-rw-r--r--
gdbm.html	19.35 KB	-rw-r--r--
gensuitemodule.html	14.54 KB	-rw-r--r--
getopt.html	26.56 KB	-rw-r--r--
getpass.html	12.5 KB	-rw-r--r--
gettext.html	91.32 KB	-rw-r--r--
gl.html	26.71 KB	-rw-r--r--
glob.html	15.42 KB	-rw-r--r--
grp.html	12.33 KB	-rw-r--r--
gzip.html	21.95 KB	-rw-r--r--
hashlib.html	27.4 KB	-rw-r--r--
heapq.html	36.72 KB	-rw-r--r--
hmac.html	15.97 KB	-rw-r--r--
hotshot.html	22.69 KB	-rw-r--r--
htmllib.html	29.9 KB	-rw-r--r--
htmlparser.html	45.11 KB	-rw-r--r--
httplib.html	78.55 KB	-rw-r--r--
i18n.html	10.61 KB	-rw-r--r--
ic.html	22.03 KB	-rw-r--r--
idle.html	45.74 KB	-rw-r--r--
imageop.html	20.94 KB	-rw-r--r--
imaplib.html	69.9 KB	-rw-r--r--
imgfile.html	14.91 KB	-rw-r--r--
imghdr.html	13.43 KB	-rw-r--r--
imp.html	41.48 KB	-rw-r--r--
importlib.html	10.27 KB	-rw-r--r--
imputil.html	36.11 KB	-rw-r--r--
index.html	82.54 KB	-rw-r--r--
inspect.html	64.31 KB	-rw-r--r--
internet.html	26.77 KB	-rw-r--r--
intro.html	9.76 KB	-rw-r--r--
io.html	122.3 KB	-rw-r--r--
ipc.html	17.18 KB	-rw-r--r--
itertools.html	129.91 KB	-rw-r--r--
jpeg.html	15.36 KB	-rw-r--r--
json.html	79.09 KB	-rw-r--r--
keyword.html	9.27 KB	-rw-r--r--
language.html	12.35 KB	-rw-r--r--
linecache.html	12.7 KB	-rw-r--r--
locale.html	68.54 KB	-rw-r--r--
logging.config.html	82.23 KB	-rw-r--r--
logging.handlers.html	91.96 KB	-rw-r--r--
logging.html	123.15 KB	-rw-r--r--
mac.html	24.49 KB	-rw-r--r--
macos.html	18.51 KB	-rw-r--r--
macosa.html	14.55 KB	-rw-r--r--
macostools.html	19.67 KB	-rw-r--r--
macpath.html	9.19 KB	-rw-r--r--
mailbox.html	185.53 KB	-rw-r--r--
mailcap.html	15.3 KB	-rw-r--r--
markup.html	20.37 KB	-rw-r--r--
marshal.html	19.88 KB	-rw-r--r--
math.html	50.52 KB	-rw-r--r--
md5.html	16.65 KB	-rw-r--r--
mhlib.html	30.04 KB	-rw-r--r--
mimetools.html	23.84 KB	-rw-r--r--
mimetypes.html	35.82 KB	-rw-r--r--
mimewriter.html	18.19 KB	-rw-r--r--
mimify.html	16.96 KB	-rw-r--r--
miniaeframe.html	14.5 KB	-rw-r--r--
misc.html	7.77 KB	-rw-r--r--
mm.html	10.19 KB	-rw-r--r--
mmap.html	33.52 KB	-rw-r--r--
modulefinder.html	19.85 KB	-rw-r--r--
modules.html	9.68 KB	-rw-r--r--
msilib.html	72.78 KB	-rw-r--r--
msvcrt.html	24.1 KB	-rw-r--r--
multifile.html	28.82 KB	-rw-r--r--
multiprocessing.html	423.97 KB	-rw-r--r--
mutex.html	13.56 KB	-rw-r--r--
netdata.html	19.28 KB	-rw-r--r--
netrc.html	15.51 KB	-rw-r--r--
new.html	16.1 KB	-rw-r--r--
nis.html	13.19 KB	-rw-r--r--
nntplib.html	51.08 KB	-rw-r--r--
numbers.html	40.91 KB	-rw-r--r--
numeric.html	14.85 KB	-rw-r--r--
operator.html	118.32 KB	-rw-r--r--
optparse.html	251.08 KB	-rw-r--r--
os.html	270.49 KB	-rw-r--r--
os.path.html	48.87 KB	-rw-r--r--
ossaudiodev.html	49.79 KB	-rw-r--r--
othergui.html	9.98 KB	-rw-r--r--
parser.html	44.52 KB	-rw-r--r--
pdb.html	41.44 KB	-rw-r--r--
persistence.html	16.25 KB	-rw-r--r--
pickle.html	107.94 KB	-rw-r--r--
pickletools.html	13.21 KB	-rw-r--r--
pipes.html	21.85 KB	-rw-r--r--
pkgutil.html	30.59 KB	-rw-r--r--
platform.html	40.14 KB	-rw-r--r--
plistlib.html	20.96 KB	-rw-r--r--
popen2.html	30.13 KB	-rw-r--r--
poplib.html	27.93 KB	-rw-r--r--
posix.html	17.27 KB	-rw-r--r--
posixfile.html	23.68 KB	-rw-r--r--
pprint.html	36.42 KB	-rw-r--r--
profile.html	76.65 KB	-rw-r--r--
pty.html	11.42 KB	-rw-r--r--
pwd.html	13.53 KB	-rw-r--r--
py_compile.html	13.33 KB	-rw-r--r--
pyclbr.html	18.14 KB	-rw-r--r--
pydoc.html	14.33 KB	-rw-r--r--
pyexpat.html	93.28 KB	-rw-r--r--
python.html	13.53 KB	-rw-r--r--
queue.html	29.64 KB	-rw-r--r--
quopri.html	14.5 KB	-rw-r--r--
random.html	47.78 KB	-rw-r--r--
re.html	163.11 KB	-rw-r--r--
readline.html	41.2 KB	-rw-r--r--
repr.html	24.57 KB	-rw-r--r--
resource.html	30.86 KB	-rw-r--r--
restricted.html	12.69 KB	-rw-r--r--
rexec.html	43.59 KB	-rw-r--r--
rfc822.html	51.25 KB	-rw-r--r--
rlcompleter.html	15.29 KB	-rw-r--r--
robotparser.html	15.01 KB	-rw-r--r--
runpy.html	23.55 KB	-rw-r--r--
sched.html	21.76 KB	-rw-r--r--
scrolledtext.html	10.67 KB	-rw-r--r--
select.html	50.17 KB	-rw-r--r--
sets.html	39.92 KB	-rw-r--r--
sgi.html	11.09 KB	-rw-r--r--
sgmllib.html	38.77 KB	-rw-r--r--
sha.html	14.55 KB	-rw-r--r--
shelve.html	32.93 KB	-rw-r--r--
shlex.html	38.43 KB	-rw-r--r--
shutil.html	49.49 KB	-rw-r--r--
signal.html	36.52 KB	-rw-r--r--
simplehttpserver.html	21.57 KB	-rw-r--r--
simplexmlrpcserver.html	40.41 KB	-rw-r--r--
site.html	29 KB	-rw-r--r--
smtpd.html	15.64 KB	-rw-r--r--
smtplib.html	51.86 KB	-rw-r--r--
sndhdr.html	12.05 KB	-rw-r--r--
socket.html	126.94 KB	-rw-r--r--
socketserver.html	81.38 KB	-rw-r--r--
someos.html	17.09 KB	-rw-r--r--
spwd.html	12.25 KB	-rw-r--r--
sqlite3.html	154.12 KB	-rw-r--r--
ssl.html	214.5 KB	-rw-r--r--
stat.html	41.11 KB	-rw-r--r--
statvfs.html	13.24 KB	-rw-r--r--
stdtypes.html	309.83 KB	-rw-r--r--
string.html	129.58 KB	-rw-r--r--
stringio.html	21.1 KB	-rw-r--r--
stringprep.html	21.4 KB	-rw-r--r--
strings.html	16.42 KB	-rw-r--r--
struct.html	47.68 KB	-rw-r--r--
subprocess.html	117 KB	-rw-r--r--
sun.html	7.83 KB	-rw-r--r--
sunau.html	35.43 KB	-rw-r--r--
sunaudio.html	21.05 KB	-rw-r--r--
symbol.html	9.06 KB	-rw-r--r--
symtable.html	29.03 KB	-rw-r--r--
sys.html	118.12 KB	-rw-r--r--
sysconfig.html	28.8 KB	-rw-r--r--
syslog.html	21.29 KB	-rw-r--r--
tabnanny.html	12.78 KB	-rw-r--r--
tarfile.html	99.54 KB	-rw-r--r--
telnetlib.html	30.46 KB	-rw-r--r--
tempfile.html	35.02 KB	-rw-r--r--
termios.html	19.22 KB	-rw-r--r--
test.html	61.42 KB	-rw-r--r--
textwrap.html	32.28 KB	-rw-r--r--
thread.html	22.67 KB	-rw-r--r--
threading.html	92.04 KB	-rw-r--r--
time.html	65.55 KB	-rw-r--r--
timeit.html	44.38 KB	-rw-r--r--
tix.html	56.73 KB	-rw-r--r--
tk.html	26.76 KB	-rw-r--r--
tkinter.html	86.67 KB	-rw-r--r--
token.html	27.31 KB	-rw-r--r--
tokenize.html	21.69 KB	-rw-r--r--
trace.html	33.91 KB	-rw-r--r--
traceback.html	44.22 KB	-rw-r--r--
ttk.html	123.83 KB	-rw-r--r--
tty.html	10.95 KB	-rw-r--r--
turtle.html	246.17 KB	-rw-r--r--
types.html	33.66 KB	-rw-r--r--
undoc.html	25.54 KB	-rw-r--r--
unicodedata.html	22.64 KB	-rw-r--r--
unittest.html	246.75 KB	-rw-r--r--
unix.html	11.9 KB	-rw-r--r--
urllib.html	71.61 KB	-rw-r--r--
urllib2.html	128.77 KB	-rw-r--r--
urlparse.html	49.04 KB	-rw-r--r--
user.html	13.41 KB	-rw-r--r--
userdict.html	32.96 KB	-rw-r--r--
uu.html	13.25 KB	-rw-r--r--
uuid.html	33.55 KB	-rw-r--r--
warnings.html	51.86 KB	-rw-r--r--
wave.html	29.08 KB	-rw-r--r--
weakref.html	41.14 KB	-rw-r--r--
webbrowser.html	29.53 KB	-rw-r--r--
whichdb.html	10.44 KB	-rw-r--r--
windows.html	10.37 KB	-rw-r--r--
winsound.html	22.56 KB	-rw-r--r--
wsgiref.html	94.38 KB	-rw-r--r--
xdrlib.html	38.05 KB	-rw-r--r--
xml.dom.html	110.39 KB	-rw-r--r--
xml.dom.minidom.html	45.23 KB	-rw-r--r--
xml.dom.pulldom.html	16.32 KB	-rw-r--r--
xml.etree.elementtree.html	124.2 KB	-rw-r--r--
xml.html	18.76 KB	-rw-r--r--
xml.sax.handler.html	47.5 KB	-rw-r--r--
xml.sax.html	26.04 KB	-rw-r--r--
xml.sax.reader.html	51.4 KB	-rw-r--r--
xml.sax.utils.html	18.11 KB	-rw-r--r--
xmlrpclib.html	71.79 KB	-rw-r--r--
zipfile.html	67.26 KB	-rw-r--r--
zipimport.html	24.32 KB	-rw-r--r--
zlib.html	34.41 KB	-rw-r--r--

Code Editor : shelve.html

<!DOCTYPE html>

<title>11.4. shelve — Python object persistence &#8212; Python 2.7.18 documentation</title>
 <link rel="stylesheet" type="text/css" href="../_static/pygments.css" />
 <link rel="stylesheet" type="text/css" href="../_static/classic.css" />
 
 <script data-url_root="../" id="documentation_options" src="../_static/documentation_options.js"></script>
 <script src="../_static/jquery.js"></script>
 <script src="../_static/underscore.js"></script>
 <script src="../_static/doctools.js"></script>
 
 <script src="../_static/sidebar.js"></script>
 
 <link rel="search" type="application/opensearchdescription+xml"
 title="Search within Python 2.7.18 documentation"
 href="../_static/opensearch.xml"/>
 <link rel="author" title="About these documents" href="../about.html" />
 <link rel="index" title="Index" href="../genindex.html" />
 <link rel="search" title="Search" href="../search.html" />
 <link rel="copyright" title="Copyright" href="../copyright.html" />
 <link rel="next" title="11.5. marshal — Internal Python object serialization" href="marshal.html" />
 <link rel="prev" title="11.3. copy_reg — Register pickle support functions" href="copy_reg.html" />
 <link rel="shortcut icon" type="image/png" href="../_static/py.png" />
 <link rel="canonical" href="file:///usr/share/doc/python2.7/html/library/shelve.html" />
 <script type="text/javascript" src="../_static/copybutton.js"></script>

</head><body>
<div id="outdated-warning" style="padding: .5em; text-align: center; background-color: #FFBABA; color: #6A0E0E;">
 This document is for an old version of Python that is <a href="https://devguide.python.org/devcycle/#end-of-life-branches">no longer supported</a>.
 You should install the python3 and python3-doc packages and read the 
 <a href="file:///usr/share/doc/python3-doc/html/library/shelve.html"> Python documentation for the Python3 version packaged in this release</a>.
</div>
 
 <div class="related" role="navigation" aria-label="related navigation">
 <h3>Navigation</h3>
 <ul>
 <li class="right" style="margin-right: 10px">
 <a href="../genindex.html" title="General Index"
 accesskey="I">index</a></li>
 <li class="right" >
 <a href="../py-modindex.html" title="Python Module Index"
 >modules</a> |</li>
 <li class="right" >
 <a href="marshal.html" title="11.5. marshal — Internal Python object serialization"
 accesskey="N">next</a> |</li>
 <li class="right" >
 <a href="copy_reg.html" title="11.3. copy_reg — Register pickle support functions"
 accesskey="P">previous</a> |</li>
 <li><img src="../_static/py.png" alt=""
 style="vertical-align: middle; margin-top: -1px"/></li>
 <li><a href="https://www.python.org/">Python</a> &#187;</li>
 <li>
 <a href="../index.html">Python 2.7.18 documentation</a> &#187;
 </li>

<li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> &#187;</li>
 <li class="nav-item nav-item-2"><a href="persistence.html" accesskey="U">11. Data Persistence</a> &#187;</li>
 <li class="nav-item nav-item-this"><a href="">11.4. <code class="xref py py-mod docutils literal notranslate">shelve</code> — Python object persistence</a></li> 
 </ul>
 </div>

<div class="document">
 <div class="documentwrapper">
 <div class="bodywrapper">
 <div class="body" role="main">
 
 <section id="module-shelve">
<h1>11.4. <a class="reference internal" href="#module-shelve" title="shelve: Python object persistence."><code class="xref py py-mod docutils literal notranslate">shelve</code></a> — Python object persistence<a class="headerlink" href="#module-shelve" title="Permalink to this headline">¶</a></h1>
Source code: <a class="reference external" href="https://github.com/python/cpython/tree/2.7/Lib/shelve.py">Lib/shelve.py</a>
<hr class="docutils" />
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 <a class="reference internal" href="pickle.html#module-pickle" title="pickle: Convert Python objects to streams of bytes and back."><code class="xref py py-mod docutils literal notranslate">pickle</code></a> module can handle.
This includes most class instances, recursive data types, and objects containing
lots of shared sub-objects. The keys are ordinary strings.
<dl class="py function">
<dt class="sig sig-object py" id="shelve.open">
shelve.open(filename, flag='c', protocol=None, writeback=False)<a class="headerlink" href="#shelve.open" title="Permalink to this definition">¶</a></dt>
<dd>Open a persistent dictionary. The filename specified is the base filename for
the underlying database. As a side-effect, an extension may be added to the
filename and more than one file may be created. By default, the underlying
database file is opened for reading and writing. The optional flag parameter
has the same interpretation as the flag parameter of <a class="reference internal" href="anydbm.html#anydbm.open" title="anydbm.open"><code class="xref py py-func docutils literal notranslate">anydbm.open()</code></a>.
By default, version 0 pickles are used to serialize values. The version of the
pickle protocol can be specified with the protocol parameter.
<div class="versionchanged">
Changed in version 2.3: The protocol parameter was added.
</div>
Because of Python semantics, a shelf cannot know when a mutable
persistent-dictionary entry is modified. By default modified objects are
written only when assigned to the shelf (see <a class="reference internal" href="#shelve-example">Example</a>). If the
optional writeback parameter is set to <code class="docutils literal notranslate">True</code>, all entries accessed are also
cached in memory, and written back on <a class="reference internal" href="#shelve.Shelf.sync" title="shelve.Shelf.sync"><code class="xref py py-meth docutils literal notranslate">sync()</code></a> and
<a class="reference internal" href="#shelve.Shelf.close" title="shelve.Shelf.close"><code class="xref py py-meth docutils literal notranslate">close()</code></a>; this can make it handier to mutate mutable entries in
the persistent dictionary, but, if many entries are accessed, it can consume
vast amounts of memory for the cache, and it can make the close operation
very slow since all accessed entries are written back (there is no way to
determine which accessed entries are mutable, nor which ones were actually
mutated).
Like file objects, shelve objects should be closed explicitly to ensure
that the persistent data is flushed to disk.
</dd></dl>

<div class="admonition warning">
Warning
Because the <a class="reference internal" href="#module-shelve" title="shelve: Python object persistence."><code class="xref py py-mod docutils literal notranslate">shelve</code></a> module is backed by <a class="reference internal" href="pickle.html#module-pickle" title="pickle: Convert Python objects to streams of bytes and back."><code class="xref py py-mod docutils literal notranslate">pickle</code></a>, it is insecure
to load a shelf from an untrusted source. Like with pickle, loading a shelf
can execute arbitrary code.
</div>
Shelf objects support most of the methods supported by dictionaries. This
eases the transition from dictionary based scripts to those requiring
persistent storage.
Note, the Python 3 transition methods (<a class="reference internal" href="stdtypes.html#dict.viewkeys" title="dict.viewkeys"><code class="xref py py-meth docutils literal notranslate">viewkeys()</code></a>,
<a class="reference internal" href="stdtypes.html#dict.viewvalues" title="dict.viewvalues"><code class="xref py py-meth docutils literal notranslate">viewvalues()</code></a>, and <a class="reference internal" href="stdtypes.html#dict.viewitems" title="dict.viewitems"><code class="xref py py-meth docutils literal notranslate">viewitems()</code></a>) are not supported.
Two additional methods are supported:
<dl class="py method">
<dt class="sig sig-object py" id="shelve.Shelf.sync">
Shelf.sync()<a class="headerlink" href="#shelve.Shelf.sync" title="Permalink to this definition">¶</a></dt>
<dd>Write back all entries in the cache if the shelf was opened with writeback
set to <a class="reference internal" href="constants.html#True" title="True"><code class="xref py py-const docutils literal notranslate">True</code></a>. Also empty the cache and synchronize the persistent
dictionary on disk, if feasible. This is called automatically when the shelf
is closed with <a class="reference internal" href="#shelve.Shelf.close" title="shelve.Shelf.close"><code class="xref py py-meth docutils literal notranslate">close()</code></a>.
</dd></dl>

<dl class="py method">
<dt class="sig sig-object py" id="shelve.Shelf.close">
Shelf.close()<a class="headerlink" href="#shelve.Shelf.close" title="Permalink to this definition">¶</a></dt>
<dd>Synchronize and close the persistent dict object. Operations on a closed
shelf will fail with a <code class="xref py py-exc docutils literal notranslate">ValueError</code>.
</dd></dl>

<div class="admonition seealso">
See also
<a class="reference external" href="https://code.activestate.com/recipes/576642/">Persistent dictionary recipe</a>
with widely supported storage formats and having the speed of native
dictionaries.
</div>
<section id="restrictions">
<h2>11.4.1. Restrictions<a class="headerlink" href="#restrictions" title="Permalink to this headline">¶</a></h2>
<blockquote>
<div></div></blockquote>
<ul class="simple" id="index-1">
<li>The choice of which database package will be used (such as <a class="reference internal" href="dbm.html#module-dbm" title="dbm: The standard &quot;database&quot; interface, based on ndbm. (Unix)"><code class="xref py py-mod docutils literal notranslate">dbm</code></a>,
<a class="reference internal" href="gdbm.html#module-gdbm" title="gdbm: GNU's reinterpretation of dbm. (Unix)"><code class="xref py py-mod docutils literal notranslate">gdbm</code></a> or <a class="reference internal" href="bsddb.html#module-bsddb" title="bsddb: Interface to Berkeley DB database library"><code class="xref py py-mod docutils literal notranslate">bsddb</code></a>) depends on which interface is available. Therefore
it is not safe to open the database directly using <a class="reference internal" href="dbm.html#module-dbm" title="dbm: The standard &quot;database&quot; interface, based on ndbm. (Unix)"><code class="xref py py-mod docutils literal notranslate">dbm</code></a>. The database is
also (unfortunately) subject to the limitations of <a class="reference internal" href="dbm.html#module-dbm" title="dbm: The standard &quot;database&quot; interface, based on ndbm. (Unix)"><code class="xref py py-mod docutils literal notranslate">dbm</code></a>, if it is used —
this means that (the pickled representation of) the objects stored in the
database should be fairly small, and in rare cases key collisions may cause the
database to refuse updates.</li>
<li>The <a class="reference internal" href="#module-shelve" title="shelve: Python object persistence."><code class="xref py py-mod docutils literal notranslate">shelve</code></a> module does not support concurrent read/write access to
shelved objects. (Multiple simultaneous read accesses are safe.) When a
program has a shelf open for writing, no other program should have it open for
reading or writing. Unix file locking can be used to solve this, but this
differs across Unix versions and requires knowledge about the database
implementation used.</li>
</ul>
<dl class="py class">
<dt class="sig sig-object py" id="shelve.Shelf">
class shelve.Shelf(dict, protocol=None, writeback=False)<a class="headerlink" href="#shelve.Shelf" title="Permalink to this definition">¶</a></dt>
<dd>A subclass of <a class="reference internal" href="userdict.html#UserDict.DictMixin" title="UserDict.DictMixin"><code class="xref py py-class docutils literal notranslate">UserDict.DictMixin</code></a> which stores pickled values in the
dict object.
By default, version 0 pickles are used to serialize values. The version of the
pickle protocol can be specified with the protocol parameter. See the
<a class="reference internal" href="pickle.html#module-pickle" title="pickle: Convert Python objects to streams of bytes and back."><code class="xref py py-mod docutils literal notranslate">pickle</code></a> documentation for a discussion of the pickle protocols.
<div class="versionchanged">
Changed in version 2.3: The protocol parameter was added.
</div>
If the writeback parameter is <code class="docutils literal notranslate">True</code>, the object will hold a cache of all
entries accessed and write them back to the dict at sync and close times.
This allows natural operations on mutable entries, but can consume much more
memory and make sync and close take a long time.
</dd></dl>

<dl class="py class">
<dt class="sig sig-object py" id="shelve.BsdDbShelf">
class shelve.BsdDbShelf(dict, protocol=None, writeback=False)<a class="headerlink" href="#shelve.BsdDbShelf" title="Permalink to this definition">¶</a></dt>
<dd>A subclass of <a class="reference internal" href="#shelve.Shelf" title="shelve.Shelf"><code class="xref py py-class docutils literal notranslate">Shelf</code></a> which exposes <code class="xref py py-meth docutils literal notranslate">first()</code>, <code class="xref py py-meth docutils literal notranslate">next()</code>,
<code class="xref py py-meth docutils literal notranslate">previous()</code>, <code class="xref py py-meth docutils literal notranslate">last()</code> and <code class="xref py py-meth docutils literal notranslate">set_location()</code> which are available in
the <a class="reference internal" href="bsddb.html#module-bsddb" title="bsddb: Interface to Berkeley DB database library"><code class="xref py py-mod docutils literal notranslate">bsddb</code></a> module but not in other database modules. The dict object
passed to the constructor must support those methods. This is generally
accomplished by calling one of <a class="reference internal" href="bsddb.html#bsddb.hashopen" title="bsddb.hashopen"><code class="xref py py-func docutils literal notranslate">bsddb.hashopen()</code></a>, <a class="reference internal" href="bsddb.html#bsddb.btopen" title="bsddb.btopen"><code class="xref py py-func docutils literal notranslate">bsddb.btopen()</code></a> or
<a class="reference internal" href="bsddb.html#bsddb.rnopen" title="bsddb.rnopen"><code class="xref py py-func docutils literal notranslate">bsddb.rnopen()</code></a>. The optional protocol and writeback parameters have
the same interpretation as for the <a class="reference internal" href="#shelve.Shelf" title="shelve.Shelf"><code class="xref py py-class docutils literal notranslate">Shelf</code></a> class.
</dd></dl>

<dl class="py class">
<dt class="sig sig-object py" id="shelve.DbfilenameShelf">
class shelve.DbfilenameShelf(filename, flag='c', protocol=None, writeback=False)<a class="headerlink" href="#shelve.DbfilenameShelf" title="Permalink to this definition">¶</a></dt>
<dd>A subclass of <a class="reference internal" href="#shelve.Shelf" title="shelve.Shelf"><code class="xref py py-class docutils literal notranslate">Shelf</code></a> which accepts a filename instead of a dict-like
object. The underlying file will be opened using <a class="reference internal" href="anydbm.html#anydbm.open" title="anydbm.open"><code class="xref py py-func docutils literal notranslate">anydbm.open()</code></a>. By
default, the file will be created and opened for both read and write. The
optional flag parameter has the same interpretation as for the <a class="reference internal" href="#shelve.open" title="shelve.open"><code class="xref py py-func docutils literal notranslate">open()</code></a>
function. The optional protocol and writeback parameters have the same
interpretation as for the <a class="reference internal" href="#shelve.Shelf" title="shelve.Shelf"><code class="xref py py-class docutils literal notranslate">Shelf</code></a> class.
</dd></dl>

</section>
<section id="example">
<h2>11.4.2. Example<a class="headerlink" href="#example" title="Permalink to this headline">¶</a></h2>
To summarize the interface (<code class="docutils literal notranslate">key</code> is a string, <code class="docutils literal notranslate">data</code> is an arbitrary
object):
<div class="highlight-default notranslate"><div class="highlight"><pre>import shelve

d = shelve.open(filename) # open -- file may get suffix added by low-level
 # library

d[key] = data # store data at key (overwrites old data if
 # using an existing key)
data = d[key] # retrieve a COPY of 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
klist = d.keys() # a list of all existing keys (slow!)

# as d was opened WITHOUT writeback=True, beware:
d[&#39;xx&#39;] = range(4) # this works as expected, but...
d[&#39;xx&#39;].append(5) # *this doesn&#39;t!* -- d[&#39;xx&#39;] is STILL range(4)!

# having opened d without writeback=True, you need to code carefully:
temp = d[&#39;xx&#39;] # extracts the copy
temp.append(5) # mutates the copy
d[&#39;xx&#39;] = temp # stores the copy right back, to persist it

# or, d=shelve.open(filename,writeback=True) would let you just code
# d[&#39;xx&#39;].append(5) and have it work as expected, BUT it would also
# consume more memory and make the d.close() operation slower.

d.close() # close it
</pre></div>
</div>
<div class="admonition seealso">
See also
<dl class="simple">
<dt>Module <a class="reference internal" href="anydbm.html#module-anydbm" title="anydbm: Generic interface to DBM-style database modules."><code class="xref py py-mod docutils literal notranslate">anydbm</code></a></dt><dd>Generic interface to <code class="docutils literal notranslate">dbm</code>-style databases.
</dd>
<dt>Module <a class="reference internal" href="bsddb.html#module-bsddb" title="bsddb: Interface to Berkeley DB database library"><code class="xref py py-mod docutils literal notranslate">bsddb</code></a></dt><dd>BSD <code class="docutils literal notranslate">db</code> database interface.
</dd>
<dt>Module <a class="reference internal" href="dbhash.html#module-dbhash" title="dbhash: DBM-style interface to the BSD database library."><code class="xref py py-mod docutils literal notranslate">dbhash</code></a></dt><dd>Thin layer around the <a class="reference internal" href="bsddb.html#module-bsddb" title="bsddb: Interface to Berkeley DB database library"><code class="xref py py-mod docutils literal notranslate">bsddb</code></a> which provides an <a class="reference internal" href="dbhash.html#dbhash.open" title="dbhash.open"><code class="xref py py-func docutils literal notranslate">open()</code></a>
function like the other database modules.
</dd>
<dt>Module <a class="reference internal" href="dbm.html#module-dbm" title="dbm: The standard &quot;database&quot; interface, based on ndbm. (Unix)"><code class="xref py py-mod docutils literal notranslate">dbm</code></a></dt><dd>Standard Unix database interface.
</dd>
<dt>Module <a class="reference internal" href="dumbdbm.html#module-dumbdbm" title="dumbdbm: Portable implementation of the simple DBM interface."><code class="xref py py-mod docutils literal notranslate">dumbdbm</code></a></dt><dd>Portable implementation of the <code class="docutils literal notranslate">dbm</code> interface.
</dd>
<dt>Module <a class="reference internal" href="gdbm.html#module-gdbm" title="gdbm: GNU's reinterpretation of dbm. (Unix)"><code class="xref py py-mod docutils literal notranslate">gdbm</code></a></dt><dd>GNU database interface, based on the <code class="docutils literal notranslate">dbm</code> interface.
</dd>
<dt>Module <a class="reference internal" href="pickle.html#module-pickle" title="pickle: Convert Python objects to streams of bytes and back."><code class="xref py py-mod docutils literal notranslate">pickle</code></a></dt><dd>Object serialization used by <a class="reference internal" href="#module-shelve" title="shelve: Python object persistence."><code class="xref py py-mod docutils literal notranslate">shelve</code></a>.
</dd>
<dt>Module <a class="reference internal" href="pickle.html#module-cPickle" title="cPickle: Faster version of pickle, but not subclassable."><code class="xref py py-mod docutils literal notranslate">cPickle</code></a></dt><dd>High-performance version of <a class="reference internal" href="pickle.html#module-pickle" title="pickle: Convert Python objects to streams of bytes and back."><code class="xref py py-mod docutils literal notranslate">pickle</code></a>.
</dd>
</dl>
</div>
</section>
</section>

<div class="clearer"></div>
 </div>
 </div>
 </div>
 <div class="sphinxsidebar" role="navigation" aria-label="main navigation">
 <div class="sphinxsidebarwrapper">
 <h3><a href="../contents.html">Table of Contents</a></h3>
 <ul>
<li><a class="reference internal" href="#">11.4. <code class="xref py py-mod docutils literal notranslate">shelve</code> — Python object persistence</a><ul>
<li><a class="reference internal" href="#restrictions">11.4.1. Restrictions</a></li>
<li><a class="reference internal" href="#example">11.4.2. Example</a></li>
</ul>
</li>
</ul>

<h4>Previous topic</h4>
 <a href="copy_reg.html"
 title="previous chapter">11.3. <code class="xref py py-mod docutils literal notranslate">copy_reg</code> — Register <code class="xref py py-mod docutils literal notranslate">pickle</code> support functions</a>
 <h4>Next topic</h4>
 <a href="marshal.html"
 title="next chapter">11.5. <code class="xref py py-mod docutils literal notranslate">marshal</code> — Internal Python object serialization</a>
 <div role="note" aria-label="source link">
 <h3>This Page</h3>
 <ul class="this-page-menu">
 <li><a href="../_sources/library/shelve.rst.txt"
 rel="nofollow">Show Source</a></li>
 </ul>
 </div>
<div id="searchbox" style="display: none" role="search">
 <h3 id="searchlabel">Quick search</h3>
 <div class="searchformwrapper">
 <form class="search" action="../search.html" method="get">
 <input type="text" name="q" aria-labelledby="searchlabel" autocomplete="off" autocorrect="off" autocapitalize="off" spellcheck="false"/>
 <input type="submit" value="Go" />
 </form>
 </div>
</div>
<script>$('#searchbox').show(0);</script>
 </div>
 </div>
 <div class="clearer"></div>
 </div> 
 <div class="related" role="navigation" aria-label="related navigation">
 <h3>Navigation</h3>
 <ul>
 <li class="right" style="margin-right: 10px">
 <a href="../genindex.html" title="General Index"
 >index</a></li>
 <li class="right" >
 <a href="../py-modindex.html" title="Python Module Index"
 >modules</a> |</li>
 <li class="right" >
 <a href="marshal.html" title="11.5. marshal — Internal Python object serialization"
 >next</a> |</li>
 <li class="right" >
 <a href="copy_reg.html" title="11.3. copy_reg — Register pickle support functions"
 >previous</a> |</li>
 <li><img src="../_static/py.png" alt=""
 style="vertical-align: middle; margin-top: -1px"/></li>
 <li><a href="https://www.python.org/">Python</a> &#187;</li>
 <li>
 <a href="../index.html">Python 2.7.18 documentation</a> &#187;
 </li>

<li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> &#187;</li>
 <li class="nav-item nav-item-2"><a href="persistence.html" >11. Data Persistence</a> &#187;</li>
 <li class="nav-item nav-item-this"><a href="">11.4. <code class="xref py py-mod docutils literal notranslate">shelve</code> — Python object persistence</a></li> 
 </ul>
 </div> 
 <div class="footer">
 &copy; <a href="../copyright.html">Copyright</a> 1990-2024, Python Software Foundation.
 
 The Python Software Foundation is a non-profit corporation.
 <a href="https://www.python.org/psf/donations/">Please donate.</a>
 
 Last updated on December 09, 2024.
 <a href="../bugs.html">Found a bug</a>?
 
 Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 4.3.2.
 </div>

</body>
</html>

${this.title}

Code Editor : shelve.html