projects / OpenSPARC-T2-SAM / blame
| Commit | Line | Data |
|---|---|---|
| 920dae64 AT |
1 | <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> |
| 2 | <html> | |
| 3 | <head> | |
| 4 | <link rel="STYLESHEET" href="lib.css" type='text/css' /> | |
| 5 | <link rel="SHORTCUT ICON" href="../icons/pyfav.png" type="image/png" /> | |
| 6 | <link rel='start' href='../index.html' title='Python Documentation Index' /> | |
| 7 | <link rel="first" href="lib.html" title='Python Library Reference' /> | |
| 8 | <link rel='contents' href='contents.html' title="Contents" /> | |
| 9 | <link rel='index' href='genindex.html' title='Index' /> | |
| 10 | <link rel='last' href='about.html' title='About this document...' /> | |
| 11 | <link rel='help' href='about.html' title='About this document...' /> | |
| 12 | <link rel="next" href="pickle-example.html" /> | |
| 13 | <link rel="prev" href="pickle-protocol.html" /> | |
| 14 | <link rel="parent" href="module-pickle.html" /> | |
| 15 | <link rel="next" href="pickle-example.html" /> | |
| 16 | <meta name='aesop' content='information' /> | |
| 17 | <title>3.14.6 Subclassing Unpicklers </title> | |
| 18 | </head> | |
| 19 | <body> | |
| 20 | <DIV CLASS="navigation"> | |
| 21 | <div id='top-navigation-panel' xml:id='top-navigation-panel'> | |
| 22 | <table align="center" width="100%" cellpadding="0" cellspacing="2"> | |
| 23 | <tr> | |
| 24 | <td class='online-navigation'><a rel="prev" title="3.14.5.3 Pickling and unpickling" | |
| 25 | href="node70.html"><img src='../icons/previous.png' | |
| 26 | border='0' height='32' alt='Previous Page' width='32' /></A></td> | |
| 27 | <td class='online-navigation'><a rel="parent" title="3.14 pickle " | |
| 28 | href="module-pickle.html"><img src='../icons/up.png' | |
| 29 | border='0' height='32' alt='Up One Level' width='32' /></A></td> | |
| 30 | <td class='online-navigation'><a rel="next" title="3.14.7 Example" | |
| 31 | href="pickle-example.html"><img src='../icons/next.png' | |
| 32 | border='0' height='32' alt='Next Page' width='32' /></A></td> | |
| 33 | <td align="center" width="100%">Python Library Reference</td> | |
| 34 | <td class='online-navigation'><a rel="contents" title="Table of Contents" | |
| 35 | href="contents.html"><img src='../icons/contents.png' | |
| 36 | border='0' height='32' alt='Contents' width='32' /></A></td> | |
| 37 | <td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png' | |
| 38 | border='0' height='32' alt='Module Index' width='32' /></a></td> | |
| 39 | <td class='online-navigation'><a rel="index" title="Index" | |
| 40 | href="genindex.html"><img src='../icons/index.png' | |
| 41 | border='0' height='32' alt='Index' width='32' /></A></td> | |
| 42 | </tr></table> | |
| 43 | <div class='online-navigation'> | |
| 44 | <b class="navlabel">Previous:</b> | |
| 45 | <a class="sectref" rel="prev" href="node70.html">3.14.5.3 Pickling and unpickling</A> | |
| 46 | <b class="navlabel">Up:</b> | |
| 47 | <a class="sectref" rel="parent" href="module-pickle.html">3.14 pickle </A> | |
| 48 | <b class="navlabel">Next:</b> | |
| 49 | <a class="sectref" rel="next" href="pickle-example.html">3.14.7 Example</A> | |
| 50 | </div> | |
| 51 | <hr /></div> | |
| 52 | </DIV> | |
| 53 | <!--End of Navigation Panel--> | |
| 54 | ||
| 55 | <H2><A NAME="SECTION0051460000000000000000"></A><A NAME="pickle-sub"></A> | |
| 56 | <BR> | |
| 57 | 3.14.6 Subclassing Unpicklers | |
| 58 | </H2> | |
| 59 | ||
| 60 | <P> | |
| 61 | By default, unpickling will import any class that it finds in the | |
| 62 | pickle data. You can control exactly what gets unpickled and what | |
| 63 | gets called by customizing your unpickler. Unfortunately, exactly how | |
| 64 | you do this is different depending on whether you're using | |
| 65 | <tt class="module">pickle</tt> or <tt class="module">cPickle</tt>.<A NAME="tex2html22" | |
| 66 | HREF="#foot8987"><SUP>3.10</SUP></A> | |
| 67 | <P> | |
| 68 | In the <tt class="module">pickle</tt> module, you need to derive a subclass from | |
| 69 | <tt class="class">Unpickler</tt>, overriding the <tt class="method">load_global()</tt> | |
| 70 | method. <tt class="method">load_global()</tt> should read two lines from the pickle | |
| 71 | data stream where the first line will the name of the module | |
| 72 | containing the class and the second line will be the name of the | |
| 73 | instance's class. It then looks up the class, possibly importing the | |
| 74 | module and digging out the attribute, then it appends what it finds to | |
| 75 | the unpickler's stack. Later on, this class will be assigned to the | |
| 76 | <tt class="member">__class__</tt> attribute of an empty class, as a way of magically | |
| 77 | creating an instance without calling its class's <tt class="method">__init__()</tt>. | |
| 78 | Your job (should you choose to accept it), would be to have | |
| 79 | <tt class="method">load_global()</tt> push onto the unpickler's stack, a known safe | |
| 80 | version of any class you deem safe to unpickle. It is up to you to | |
| 81 | produce such a class. Or you could raise an error if you want to | |
| 82 | disallow all unpickling of instances. If this sounds like a hack, | |
| 83 | you're right. Refer to the source code to make this work. | |
| 84 | ||
| 85 | <P> | |
| 86 | Things are a little cleaner with <tt class="module">cPickle</tt>, but not by much. | |
| 87 | To control what gets unpickled, you can set the unpickler's | |
| 88 | <tt class="member">find_global</tt> attribute to a function or <code>None</code>. If it is | |
| 89 | <code>None</code> then any attempts to unpickle instances will raise an | |
| 90 | <tt class="exception">UnpicklingError</tt>. If it is a function, | |
| 91 | then it should accept a module name and a class name, and return the | |
| 92 | corresponding class object. It is responsible for looking up the | |
| 93 | class and performing any necessary imports, and it may raise an | |
| 94 | error to prevent instances of the class from being unpickled. | |
| 95 | ||
| 96 | <P> | |
| 97 | The moral of the story is that you should be really careful about the | |
| 98 | source of the strings your application unpickles. | |
| 99 | ||
| 100 | <P> | |
| 101 | <BR><HR><H4>Footnotes</H4> | |
| 102 | <DL> | |
| 103 | <DT><A NAME="foot8987">...cPickle.</A><A | |
| 104 | href="pickle-sub.html#tex2html22"><SUP>3.10</SUP></A></DT> | |
| 105 | <DD>A word of caution: the | |
| 106 | mechanisms described here use internal attributes and methods, which | |
| 107 | are subject to change in future versions of Python. We intend to | |
| 108 | someday provide a common interface for controlling this behavior, | |
| 109 | which will work in either <tt class="module">pickle</tt> or <tt class="module">cPickle</tt>. | |
| 110 | ||
| 111 | </DD> | |
| 112 | </DL> | |
| 113 | <DIV CLASS="navigation"> | |
| 114 | <div class='online-navigation'> | |
| 115 | <p></p><hr /> | |
| 116 | <table align="center" width="100%" cellpadding="0" cellspacing="2"> | |
| 117 | <tr> | |
| 118 | <td class='online-navigation'><a rel="prev" title="3.14.5.3 Pickling and unpickling" | |
| 119 | href="node70.html"><img src='../icons/previous.png' | |
| 120 | border='0' height='32' alt='Previous Page' width='32' /></A></td> | |
| 121 | <td class='online-navigation'><a rel="parent" title="3.14 pickle " | |
| 122 | href="module-pickle.html"><img src='../icons/up.png' | |
| 123 | border='0' height='32' alt='Up One Level' width='32' /></A></td> | |
| 124 | <td class='online-navigation'><a rel="next" title="3.14.7 Example" | |
| 125 | href="pickle-example.html"><img src='../icons/next.png' | |
| 126 | border='0' height='32' alt='Next Page' width='32' /></A></td> | |
| 127 | <td align="center" width="100%">Python Library Reference</td> | |
| 128 | <td class='online-navigation'><a rel="contents" title="Table of Contents" | |
| 129 | href="contents.html"><img src='../icons/contents.png' | |
| 130 | border='0' height='32' alt='Contents' width='32' /></A></td> | |
| 131 | <td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png' | |
| 132 | border='0' height='32' alt='Module Index' width='32' /></a></td> | |
| 133 | <td class='online-navigation'><a rel="index" title="Index" | |
| 134 | href="genindex.html"><img src='../icons/index.png' | |
| 135 | border='0' height='32' alt='Index' width='32' /></A></td> | |
| 136 | </tr></table> | |
| 137 | <div class='online-navigation'> | |
| 138 | <b class="navlabel">Previous:</b> | |
| 139 | <a class="sectref" rel="prev" href="node70.html">3.14.5.3 Pickling and unpickling</A> | |
| 140 | <b class="navlabel">Up:</b> | |
| 141 | <a class="sectref" rel="parent" href="module-pickle.html">3.14 pickle </A> | |
| 142 | <b class="navlabel">Next:</b> | |
| 143 | <a class="sectref" rel="next" href="pickle-example.html">3.14.7 Example</A> | |
| 144 | </div> | |
| 145 | </div> | |
| 146 | <hr /> | |
| 147 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> | |
| 148 | </DIV> | |
| 149 | <!--End of Navigation Panel--> | |
| 150 | <ADDRESS> | |
| 151 | See <i><a href="about.html">About this document...</a></i> for information on suggesting changes. | |
| 152 | </ADDRESS> | |
| 153 | </BODY> | |
| 154 | </HTML> |