sam-t2/devtools/amd64/html/python/lib/node77.html

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<link rel="STYLESHEET" href="lib.css" type='text/css' />
<link rel="SHORTCUT ICON" href="../icons/pyfav.png" type="image/png" />
<link rel='start' href='../index.html' title='Python Documentation Index' />
<link rel="first" href="lib.html" title='Python Library Reference' />
<link rel='contents' href='contents.html' title="Contents" />
<link rel='index' href='genindex.html' title='Index' />
<link rel='last' href='about.html' title='About this document...' />
<link rel='help' href='about.html' title='About this document...' />
<link rel="prev" href="node76.html" />
<link rel="parent" href="module-shelve.html" />
<link rel="next" href="module-copy.html" />
<meta name='aesop' content='information' />
<title>3.17.2 Example</title>
</head>
<body>
<DIV CLASS="navigation">
<div id='top-navigation-panel' xml:id='top-navigation-panel'>
<table align="center" width="100%" cellpadding="0" cellspacing="2">
<tr>
<td class='online-navigation'><a rel="prev" title="3.17.1 Restrictions"
  href="node76.html"><img src='../icons/previous.png'
  border='0' height='32'  alt='Previous Page' width='32' /></A></td>
<td class='online-navigation'><a rel="parent" title="3.17 shelve  "
  href="module-shelve.html"><img src='../icons/up.png'
  border='0' height='32'  alt='Up One Level' width='32' /></A></td>
<td class='online-navigation'><a rel="next" title="3.18 copy  "
  href="module-copy.html"><img src='../icons/next.png'
  border='0' height='32'  alt='Next Page' width='32' /></A></td>
<td align="center" width="100%">Python Library Reference</td>
<td class='online-navigation'><a rel="contents" title="Table of Contents"
  href="contents.html"><img src='../icons/contents.png'
  border='0' height='32'  alt='Contents' width='32' /></A></td>
<td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png'
  border='0' height='32'  alt='Module Index' width='32' /></a></td>
<td class='online-navigation'><a rel="index" title="Index"
  href="genindex.html"><img src='../icons/index.png'
  border='0' height='32'  alt='Index' width='32' /></A></td>
</tr></table>
<div class='online-navigation'>
<b class="navlabel">Previous:</b>
<a class="sectref" rel="prev" href="node76.html">3.17.1 Restrictions</A>
<b class="navlabel">Up:</b>
<a class="sectref" rel="parent" href="module-shelve.html">3.17 shelve  </A>
<b class="navlabel">Next:</b>
<a class="sectref" rel="next" href="module-copy.html">3.18 copy  </A>
</div>
<hr /></div>
</DIV>
<!--End of Navigation Panel-->

<H2><A NAME="SECTION0051720000000000000000">
3.17.2 Example</A>
</H2>

<P>
To summarize the interface (<code>key</code> is a string, <code>data</code> is an
arbitrary object):

<P>
<div class="verbatim"><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
list = d.keys() # a list of all existing keys (slow!)

# as d was opened WITHOUT writeback=True, beware:
d['xx'] = range(4)  # this works as expected, but...
d['xx'].append(5)   # *this doesn't!* -- d['xx'] is STILL range(4)!!!
# having opened d without writeback=True, you need to code carefully:
temp = d['xx']      # extracts the copy
temp.append(5)      # mutates the copy
d['xx'] = temp      # stores the copy right back, to persist it
# or, d=shelve.open(filename,writeback=True) would let you just code
# d['xx'].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>

<P>
<div class="seealso">
  <p class="heading">See Also:</p>

  <dl compact="compact" class="seemodule">
    <dt>Module <b><tt class="module"><a href="module-anydbm.html">anydbm</a></tt>:</b>
    <dd>Generic interface to <code>dbm</code>-style databases.
  </dl>
  <dl compact="compact" class="seemodule">
    <dt>Module <b><tt class="module"><a href="module-bsddb.html">bsddb</a></tt>:</b>
    <dd>BSD <code>db</code> database interface.
  </dl>
  <dl compact="compact" class="seemodule">
    <dt>Module <b><tt class="module"><a href="module-dbhash.html">dbhash</a></tt>:</b>
    <dd>Thin layer around the <tt class="module">bsddb</tt> which provides an
  <tt class="function">open</tt> function like the other database modules.
  </dl>
  <dl compact="compact" class="seemodule">
    <dt>Module <b><tt class="module"><a href="module-dbm.html">dbm</a></tt>:</b>
    <dd>Standard <span class="Unix">Unix</span> database interface.
  </dl>
  <dl compact="compact" class="seemodule">
    <dt>Module <b><tt class="module"><a href="module-dumbdbm.html">dumbdbm</a></tt>:</b>
    <dd>Portable implementation of the <code>dbm</code> interface.
  </dl>
  <dl compact="compact" class="seemodule">
    <dt>Module <b><tt class="module"><a href="module-gdbm.html">gdbm</a></tt>:</b>
    <dd>GNU database interface, based on the <code>dbm</code> interface.
  </dl>
  <dl compact="compact" class="seemodule">
    <dt>Module <b><tt class="module"><a href="module-pickle.html">pickle</a></tt>:</b>
    <dd>Object serialization used by <tt class="module">shelve</tt>.
  </dl>
  <dl compact="compact" class="seemodule">
    <dt>Module <b><tt class="module"><a href="module-cPickle.html">cPickle</a></tt>:</b>
    <dd>High-performance version of <tt class="module"><a href="module-pickle.html">pickle</a></tt>.
  </dl>
</div>

<DIV CLASS="navigation">
<div class='online-navigation'>
<p></p><hr />
<table align="center" width="100%" cellpadding="0" cellspacing="2">
<tr>
<td class='online-navigation'><a rel="prev" title="3.17.1 Restrictions"
  href="node76.html"><img src='../icons/previous.png'
  border='0' height='32'  alt='Previous Page' width='32' /></A></td>
<td class='online-navigation'><a rel="parent" title="3.17 shelve  "
  href="module-shelve.html"><img src='../icons/up.png'
  border='0' height='32'  alt='Up One Level' width='32' /></A></td>
<td class='online-navigation'><a rel="next" title="3.18 copy  "
  href="module-copy.html"><img src='../icons/next.png'
  border='0' height='32'  alt='Next Page' width='32' /></A></td>
<td align="center" width="100%">Python Library Reference</td>
<td class='online-navigation'><a rel="contents" title="Table of Contents"
  href="contents.html"><img src='../icons/contents.png'
  border='0' height='32'  alt='Contents' width='32' /></A></td>
<td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png'
  border='0' height='32'  alt='Module Index' width='32' /></a></td>
<td class='online-navigation'><a rel="index" title="Index"
  href="genindex.html"><img src='../icons/index.png'
  border='0' height='32'  alt='Index' width='32' /></A></td>
</tr></table>
<div class='online-navigation'>
<b class="navlabel">Previous:</b>
<a class="sectref" rel="prev" href="node76.html">3.17.1 Restrictions</A>
<b class="navlabel">Up:</b>
<a class="sectref" rel="parent" href="module-shelve.html">3.17 shelve  </A>
<b class="navlabel">Next:</b>
<a class="sectref" rel="next" href="module-copy.html">3.18 copy  </A>
</div>
</div>
<hr />
<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
</DIV>
<!--End of Navigation Panel-->
<ADDRESS>
See <i><a href="about.html">About this document...</a></i> for information on suggesting changes.
</ADDRESS>
</BODY>
</HTML>