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<div class="section" id="module-xdrlib">
<h1>14.5. <tt class="xref docutils literal"><span class="pre">xdrlib</span></tt> — Encode and decode XDR data<a class="headerlink" href="#module-xdrlib" title="Permalink to this headline">¶</a></h1>
<p id="index-754">The <tt class="xref docutils literal"><span class="pre">xdrlib</span></tt> module supports the External Data Representation Standard as
described in <span class="target" id="index-755"></span><a class="reference external" href="http://tools.ietf.org/html/rfc1014.html"><strong>RFC 1014</strong></a>, written by Sun Microsystems, Inc. June 1987. It
supports most of the data types described in the RFC.</p>
<p>The <tt class="xref docutils literal"><span class="pre">xdrlib</span></tt> module defines two classes, one for packing variables into XDR
representation, and another for unpacking from XDR representation. There are
also two exception classes.</p>
<dl class="class">
<dt id="xdrlib.Packer">
<em class="property">class </em><tt class="descclassname">xdrlib.</tt><tt class="descname">Packer</tt><a class="headerlink" href="#xdrlib.Packer" title="Permalink to this definition">¶</a></dt>
<dd><a title="xdrlib.Packer" class="reference internal" href="#xdrlib.Packer"><tt class="xref docutils literal"><span class="pre">Packer</span></tt></a> is the class for packing data into XDR representation. The
<a title="xdrlib.Packer" class="reference internal" href="#xdrlib.Packer"><tt class="xref docutils literal"><span class="pre">Packer</span></tt></a> class is instantiated with no arguments.</dd></dl>
<dl class="class">
<dt id="xdrlib.Unpacker">
<em class="property">class </em><tt class="descclassname">xdrlib.</tt><tt class="descname">Unpacker</tt><big>(</big><em>data</em><big>)</big><a class="headerlink" href="#xdrlib.Unpacker" title="Permalink to this definition">¶</a></dt>
<dd><tt class="docutils literal"><span class="pre">Unpacker</span></tt> is the complementary class which unpacks XDR data values from a
string buffer. The input buffer is given as <em>data</em>.</dd></dl>
<div class="admonition-see-also admonition seealso">
<p class="first admonition-title">See also</p>
<dl class="last docutils">
<dt><span class="target" id="index-756"></span><a class="reference external" href="http://tools.ietf.org/html/rfc1014.html"><strong>RFC 1014</strong></a> - XDR: External Data Representation Standard</dt>
<dd>This RFC defined the encoding of data which was XDR at the time this module was
originally written. It has apparently been obsoleted by <span class="target" id="index-757"></span><a class="reference external" href="http://tools.ietf.org/html/rfc1832.html"><strong>RFC 1832</strong></a>.</dd>
<dt><span class="target" id="index-758"></span><a class="reference external" href="http://tools.ietf.org/html/rfc1832.html"><strong>RFC 1832</strong></a> - XDR: External Data Representation Standard</dt>
<dd>Newer RFC that provides a revised definition of XDR.</dd>
</dl>
</div>
<div class="section" id="packer-objects">
<span id="xdr-packer-objects"></span><h2>14.5.1. Packer Objects<a class="headerlink" href="#packer-objects" title="Permalink to this headline">¶</a></h2>
<p><a title="xdrlib.Packer" class="reference internal" href="#xdrlib.Packer"><tt class="xref docutils literal"><span class="pre">Packer</span></tt></a> instances have the following methods:</p>
<dl class="method">
<dt id="xdrlib.Packer.get_buffer">
<tt class="descclassname">Packer.</tt><tt class="descname">get_buffer</tt><big>(</big><big>)</big><a class="headerlink" href="#xdrlib.Packer.get_buffer" title="Permalink to this definition">¶</a></dt>
<dd>Returns the current pack buffer as a string.</dd></dl>
<dl class="method">
<dt id="xdrlib.Packer.reset">
<tt class="descclassname">Packer.</tt><tt class="descname">reset</tt><big>(</big><big>)</big><a class="headerlink" href="#xdrlib.Packer.reset" title="Permalink to this definition">¶</a></dt>
<dd>Resets the pack buffer to the empty string.</dd></dl>
<p>In general, you can pack any of the most common XDR data types by calling the
appropriate <tt class="docutils literal"><span class="pre">pack_type()</span></tt> method. Each method takes a single argument, the
value to pack. The following simple data type packing methods are supported:
<tt class="xref docutils literal"><span class="pre">pack_uint()</span></tt>, <tt class="xref docutils literal"><span class="pre">pack_int()</span></tt>, <tt class="xref docutils literal"><span class="pre">pack_enum()</span></tt>, <tt class="xref docutils literal"><span class="pre">pack_bool()</span></tt>,
<tt class="xref docutils literal"><span class="pre">pack_uhyper()</span></tt>, and <tt class="xref docutils literal"><span class="pre">pack_hyper()</span></tt>.</p>
<dl class="method">
<dt id="xdrlib.Packer.pack_float">
<tt class="descclassname">Packer.</tt><tt class="descname">pack_float</tt><big>(</big><em>value</em><big>)</big><a class="headerlink" href="#xdrlib.Packer.pack_float" title="Permalink to this definition">¶</a></dt>
<dd>Packs the single-precision floating point number <em>value</em>.</dd></dl>
<dl class="method">
<dt id="xdrlib.Packer.pack_double">
<tt class="descclassname">Packer.</tt><tt class="descname">pack_double</tt><big>(</big><em>value</em><big>)</big><a class="headerlink" href="#xdrlib.Packer.pack_double" title="Permalink to this definition">¶</a></dt>
<dd>Packs the double-precision floating point number <em>value</em>.</dd></dl>
<p>The following methods support packing strings, bytes, and opaque data:</p>
<dl class="method">
<dt id="xdrlib.Packer.pack_fstring">
<tt class="descclassname">Packer.</tt><tt class="descname">pack_fstring</tt><big>(</big><em>n</em>, <em>s</em><big>)</big><a class="headerlink" href="#xdrlib.Packer.pack_fstring" title="Permalink to this definition">¶</a></dt>
<dd>Packs a fixed length string, <em>s</em>. <em>n</em> is the length of the string but it is
<em>not</em> packed into the data buffer. The string is padded with null bytes if
necessary to guaranteed 4 byte alignment.</dd></dl>
<dl class="method">
<dt id="xdrlib.Packer.pack_fopaque">
<tt class="descclassname">Packer.</tt><tt class="descname">pack_fopaque</tt><big>(</big><em>n</em>, <em>data</em><big>)</big><a class="headerlink" href="#xdrlib.Packer.pack_fopaque" title="Permalink to this definition">¶</a></dt>
<dd>Packs a fixed length opaque data stream, similarly to <a title="xdrlib.Packer.pack_fstring" class="reference internal" href="#xdrlib.Packer.pack_fstring"><tt class="xref docutils literal"><span class="pre">pack_fstring()</span></tt></a>.</dd></dl>
<dl class="method">
<dt id="xdrlib.Packer.pack_string">
<tt class="descclassname">Packer.</tt><tt class="descname">pack_string</tt><big>(</big><em>s</em><big>)</big><a class="headerlink" href="#xdrlib.Packer.pack_string" title="Permalink to this definition">¶</a></dt>
<dd>Packs a variable length string, <em>s</em>. The length of the string is first packed
as an unsigned integer, then the string data is packed with
<a title="xdrlib.Packer.pack_fstring" class="reference internal" href="#xdrlib.Packer.pack_fstring"><tt class="xref docutils literal"><span class="pre">pack_fstring()</span></tt></a>.</dd></dl>
<dl class="method">
<dt id="xdrlib.Packer.pack_opaque">
<tt class="descclassname">Packer.</tt><tt class="descname">pack_opaque</tt><big>(</big><em>data</em><big>)</big><a class="headerlink" href="#xdrlib.Packer.pack_opaque" title="Permalink to this definition">¶</a></dt>
<dd>Packs a variable length opaque data string, similarly to <a title="xdrlib.Packer.pack_string" class="reference internal" href="#xdrlib.Packer.pack_string"><tt class="xref docutils literal"><span class="pre">pack_string()</span></tt></a>.</dd></dl>
<dl class="method">
<dt id="xdrlib.Packer.pack_bytes">
<tt class="descclassname">Packer.</tt><tt class="descname">pack_bytes</tt><big>(</big><em>bytes</em><big>)</big><a class="headerlink" href="#xdrlib.Packer.pack_bytes" title="Permalink to this definition">¶</a></dt>
<dd>Packs a variable length byte stream, similarly to <a title="xdrlib.Packer.pack_string" class="reference internal" href="#xdrlib.Packer.pack_string"><tt class="xref docutils literal"><span class="pre">pack_string()</span></tt></a>.</dd></dl>
<p>The following methods support packing arrays and lists:</p>
<dl class="method">
<dt id="xdrlib.Packer.pack_list">
<tt class="descclassname">Packer.</tt><tt class="descname">pack_list</tt><big>(</big><em>list</em>, <em>pack_item</em><big>)</big><a class="headerlink" href="#xdrlib.Packer.pack_list" title="Permalink to this definition">¶</a></dt>
<dd><p>Packs a <em>list</em> of homogeneous items. This method is useful for lists with an
indeterminate size; i.e. the size is not available until the entire list has
been walked. For each item in the list, an unsigned integer <tt class="docutils literal"><span class="pre">1</span></tt> is packed
first, followed by the data value from the list. <em>pack_item</em> is the function
that is called to pack the individual item. At the end of the list, an unsigned
integer <tt class="docutils literal"><span class="pre">0</span></tt> is packed.</p>
<p>For example, to pack a list of integers, the code might appear like this:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">xdrlib</span>
<span class="n">p</span> <span class="o">=</span> <span class="n">xdrlib</span><span class="o">.</span><span class="n">Packer</span><span class="p">()</span>
<span class="n">p</span><span class="o">.</span><span class="n">pack_list</span><span class="p">([</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">],</span> <span class="n">p</span><span class="o">.</span><span class="n">pack_int</span><span class="p">)</span>
</pre></div>
</div>
</dd></dl>
<dl class="method">
<dt id="xdrlib.Packer.pack_farray">
<tt class="descclassname">Packer.</tt><tt class="descname">pack_farray</tt><big>(</big><em>n</em>, <em>array</em>, <em>pack_item</em><big>)</big><a class="headerlink" href="#xdrlib.Packer.pack_farray" title="Permalink to this definition">¶</a></dt>
<dd>Packs a fixed length list (<em>array</em>) of homogeneous items. <em>n</em> is the length of
the list; it is <em>not</em> packed into the buffer, but a <a title="exceptions.ValueError" class="reference external" href="exceptions.html#exceptions.ValueError"><tt class="xref docutils literal"><span class="pre">ValueError</span></tt></a> exception
is raised if <tt class="docutils literal"><span class="pre">len(array)</span></tt> is not equal to <em>n</em>. As above, <em>pack_item</em> is the
function used to pack each element.</dd></dl>
<dl class="method">
<dt id="xdrlib.Packer.pack_array">
<tt class="descclassname">Packer.</tt><tt class="descname">pack_array</tt><big>(</big><em>list</em>, <em>pack_item</em><big>)</big><a class="headerlink" href="#xdrlib.Packer.pack_array" title="Permalink to this definition">¶</a></dt>
<dd>Packs a variable length <em>list</em> of homogeneous items. First, the length of the
list is packed as an unsigned integer, then each element is packed as in
<a title="xdrlib.Packer.pack_farray" class="reference internal" href="#xdrlib.Packer.pack_farray"><tt class="xref docutils literal"><span class="pre">pack_farray()</span></tt></a> above.</dd></dl>
</div>
<div class="section" id="unpacker-objects">
<span id="xdr-unpacker-objects"></span><h2>14.5.2. Unpacker Objects<a class="headerlink" href="#unpacker-objects" title="Permalink to this headline">¶</a></h2>
<p>The <a title="xdrlib.Unpacker" class="reference internal" href="#xdrlib.Unpacker"><tt class="xref docutils literal"><span class="pre">Unpacker</span></tt></a> class offers the following methods:</p>
<dl class="method">
<dt id="xdrlib.Unpacker.reset">
<tt class="descclassname">Unpacker.</tt><tt class="descname">reset</tt><big>(</big><em>data</em><big>)</big><a class="headerlink" href="#xdrlib.Unpacker.reset" title="Permalink to this definition">¶</a></dt>
<dd>Resets the string buffer with the given <em>data</em>.</dd></dl>
<dl class="method">
<dt id="xdrlib.Unpacker.get_position">
<tt class="descclassname">Unpacker.</tt><tt class="descname">get_position</tt><big>(</big><big>)</big><a class="headerlink" href="#xdrlib.Unpacker.get_position" title="Permalink to this definition">¶</a></dt>
<dd>Returns the current unpack position in the data buffer.</dd></dl>
<dl class="method">
<dt id="xdrlib.Unpacker.set_position">
<tt class="descclassname">Unpacker.</tt><tt class="descname">set_position</tt><big>(</big><em>position</em><big>)</big><a class="headerlink" href="#xdrlib.Unpacker.set_position" title="Permalink to this definition">¶</a></dt>
<dd>Sets the data buffer unpack position to <em>position</em>. You should be careful about
using <a title="xdrlib.Unpacker.get_position" class="reference internal" href="#xdrlib.Unpacker.get_position"><tt class="xref docutils literal"><span class="pre">get_position()</span></tt></a> and <a title="xdrlib.Unpacker.set_position" class="reference internal" href="#xdrlib.Unpacker.set_position"><tt class="xref docutils literal"><span class="pre">set_position()</span></tt></a>.</dd></dl>
<dl class="method">
<dt id="xdrlib.Unpacker.get_buffer">
<tt class="descclassname">Unpacker.</tt><tt class="descname">get_buffer</tt><big>(</big><big>)</big><a class="headerlink" href="#xdrlib.Unpacker.get_buffer" title="Permalink to this definition">¶</a></dt>
<dd>Returns the current unpack data buffer as a string.</dd></dl>
<dl class="method">
<dt id="xdrlib.Unpacker.done">
<tt class="descclassname">Unpacker.</tt><tt class="descname">done</tt><big>(</big><big>)</big><a class="headerlink" href="#xdrlib.Unpacker.done" title="Permalink to this definition">¶</a></dt>
<dd>Indicates unpack completion. Raises an <a title="xdrlib.Error" class="reference internal" href="#xdrlib.Error"><tt class="xref docutils literal"><span class="pre">Error</span></tt></a> exception if all of the
data has not been unpacked.</dd></dl>
<p>In addition, every data type that can be packed with a <a title="xdrlib.Packer" class="reference internal" href="#xdrlib.Packer"><tt class="xref docutils literal"><span class="pre">Packer</span></tt></a>, can be
unpacked with an <a title="xdrlib.Unpacker" class="reference internal" href="#xdrlib.Unpacker"><tt class="xref docutils literal"><span class="pre">Unpacker</span></tt></a>. Unpacking methods are of the form
<tt class="docutils literal"><span class="pre">unpack_type()</span></tt>, and take no arguments. They return the unpacked object.</p>
<dl class="method">
<dt id="xdrlib.Unpacker.unpack_float">
<tt class="descclassname">Unpacker.</tt><tt class="descname">unpack_float</tt><big>(</big><big>)</big><a class="headerlink" href="#xdrlib.Unpacker.unpack_float" title="Permalink to this definition">¶</a></dt>
<dd>Unpacks a single-precision floating point number.</dd></dl>
<dl class="method">
<dt id="xdrlib.Unpacker.unpack_double">
<tt class="descclassname">Unpacker.</tt><tt class="descname">unpack_double</tt><big>(</big><big>)</big><a class="headerlink" href="#xdrlib.Unpacker.unpack_double" title="Permalink to this definition">¶</a></dt>
<dd>Unpacks a double-precision floating point number, similarly to
<a title="xdrlib.Unpacker.unpack_float" class="reference internal" href="#xdrlib.Unpacker.unpack_float"><tt class="xref docutils literal"><span class="pre">unpack_float()</span></tt></a>.</dd></dl>
<p>In addition, the following methods unpack strings, bytes, and opaque data:</p>
<dl class="method">
<dt id="xdrlib.Unpacker.unpack_fstring">
<tt class="descclassname">Unpacker.</tt><tt class="descname">unpack_fstring</tt><big>(</big><em>n</em><big>)</big><a class="headerlink" href="#xdrlib.Unpacker.unpack_fstring" title="Permalink to this definition">¶</a></dt>
<dd>Unpacks and returns a fixed length string. <em>n</em> is the number of characters
expected. Padding with null bytes to guaranteed 4 byte alignment is assumed.</dd></dl>
<dl class="method">
<dt id="xdrlib.Unpacker.unpack_fopaque">
<tt class="descclassname">Unpacker.</tt><tt class="descname">unpack_fopaque</tt><big>(</big><em>n</em><big>)</big><a class="headerlink" href="#xdrlib.Unpacker.unpack_fopaque" title="Permalink to this definition">¶</a></dt>
<dd>Unpacks and returns a fixed length opaque data stream, similarly to
<a title="xdrlib.Unpacker.unpack_fstring" class="reference internal" href="#xdrlib.Unpacker.unpack_fstring"><tt class="xref docutils literal"><span class="pre">unpack_fstring()</span></tt></a>.</dd></dl>
<dl class="method">
<dt id="xdrlib.Unpacker.unpack_string">
<tt class="descclassname">Unpacker.</tt><tt class="descname">unpack_string</tt><big>(</big><big>)</big><a class="headerlink" href="#xdrlib.Unpacker.unpack_string" title="Permalink to this definition">¶</a></dt>
<dd>Unpacks and returns a variable length string. The length of the string is first
unpacked as an unsigned integer, then the string data is unpacked with
<a title="xdrlib.Unpacker.unpack_fstring" class="reference internal" href="#xdrlib.Unpacker.unpack_fstring"><tt class="xref docutils literal"><span class="pre">unpack_fstring()</span></tt></a>.</dd></dl>
<dl class="method">
<dt id="xdrlib.Unpacker.unpack_opaque">
<tt class="descclassname">Unpacker.</tt><tt class="descname">unpack_opaque</tt><big>(</big><big>)</big><a class="headerlink" href="#xdrlib.Unpacker.unpack_opaque" title="Permalink to this definition">¶</a></dt>
<dd>Unpacks and returns a variable length opaque data string, similarly to
<a title="xdrlib.Unpacker.unpack_string" class="reference internal" href="#xdrlib.Unpacker.unpack_string"><tt class="xref docutils literal"><span class="pre">unpack_string()</span></tt></a>.</dd></dl>
<dl class="method">
<dt id="xdrlib.Unpacker.unpack_bytes">
<tt class="descclassname">Unpacker.</tt><tt class="descname">unpack_bytes</tt><big>(</big><big>)</big><a class="headerlink" href="#xdrlib.Unpacker.unpack_bytes" title="Permalink to this definition">¶</a></dt>
<dd>Unpacks and returns a variable length byte stream, similarly to
<a title="xdrlib.Unpacker.unpack_string" class="reference internal" href="#xdrlib.Unpacker.unpack_string"><tt class="xref docutils literal"><span class="pre">unpack_string()</span></tt></a>.</dd></dl>
<p>The following methods support unpacking arrays and lists:</p>
<dl class="method">
<dt id="xdrlib.Unpacker.unpack_list">
<tt class="descclassname">Unpacker.</tt><tt class="descname">unpack_list</tt><big>(</big><em>unpack_item</em><big>)</big><a class="headerlink" href="#xdrlib.Unpacker.unpack_list" title="Permalink to this definition">¶</a></dt>
<dd>Unpacks and returns a list of homogeneous items. The list is unpacked one
element at a time by first unpacking an unsigned integer flag. If the flag is
<tt class="docutils literal"><span class="pre">1</span></tt>, then the item is unpacked and appended to the list. A flag of <tt class="docutils literal"><span class="pre">0</span></tt>
indicates the end of the list. <em>unpack_item</em> is the function that is called to
unpack the items.</dd></dl>
<dl class="method">
<dt id="xdrlib.Unpacker.unpack_farray">
<tt class="descclassname">Unpacker.</tt><tt class="descname">unpack_farray</tt><big>(</big><em>n</em>, <em>unpack_item</em><big>)</big><a class="headerlink" href="#xdrlib.Unpacker.unpack_farray" title="Permalink to this definition">¶</a></dt>
<dd>Unpacks and returns (as a list) a fixed length array of homogeneous items. <em>n</em>
is number of list elements to expect in the buffer. As above, <em>unpack_item</em> is
the function used to unpack each element.</dd></dl>
<dl class="method">
<dt id="xdrlib.Unpacker.unpack_array">
<tt class="descclassname">Unpacker.</tt><tt class="descname">unpack_array</tt><big>(</big><em>unpack_item</em><big>)</big><a class="headerlink" href="#xdrlib.Unpacker.unpack_array" title="Permalink to this definition">¶</a></dt>
<dd>Unpacks and returns a variable length <em>list</em> of homogeneous items. First, the
length of the list is unpacked as an unsigned integer, then each element is
unpacked as in <a title="xdrlib.Unpacker.unpack_farray" class="reference internal" href="#xdrlib.Unpacker.unpack_farray"><tt class="xref docutils literal"><span class="pre">unpack_farray()</span></tt></a> above.</dd></dl>
</div>
<div class="section" id="exceptions">
<span id="xdr-exceptions"></span><h2>14.5.3. Exceptions<a class="headerlink" href="#exceptions" title="Permalink to this headline">¶</a></h2>
<p>Exceptions in this module are coded as class instances:</p>
<dl class="exception">
<dt id="xdrlib.Error">
<em class="property">exception </em><tt class="descclassname">xdrlib.</tt><tt class="descname">Error</tt><a class="headerlink" href="#xdrlib.Error" title="Permalink to this definition">¶</a></dt>
<dd>The base exception class. <a title="xdrlib.Error" class="reference internal" href="#xdrlib.Error"><tt class="xref docutils literal"><span class="pre">Error</span></tt></a> has a single public data member
<tt class="xref docutils literal"><span class="pre">msg</span></tt> containing the description of the error.</dd></dl>
<dl class="exception">
<dt id="xdrlib.ConversionError">
<em class="property">exception </em><tt class="descclassname">xdrlib.</tt><tt class="descname">ConversionError</tt><a class="headerlink" href="#xdrlib.ConversionError" title="Permalink to this definition">¶</a></dt>
<dd>Class derived from <a title="xdrlib.Error" class="reference internal" href="#xdrlib.Error"><tt class="xref docutils literal"><span class="pre">Error</span></tt></a>. Contains no additional instance variables.</dd></dl>
<p>Here is an example of how you would catch one of these exceptions:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">import</span> <span class="nn">xdrlib</span>
<span class="n">p</span> <span class="o">=</span> <span class="n">xdrlib</span><span class="o">.</span><span class="n">Packer</span><span class="p">()</span>
<span class="k">try</span><span class="p">:</span>
<span class="n">p</span><span class="o">.</span><span class="n">pack_double</span><span class="p">(</span><span class="mf">8.01</span><span class="p">)</span>
<span class="k">except</span> <span class="n">xdrlib</span><span class="o">.</span><span class="n">ConversionError</span><span class="p">,</span> <span class="n">instance</span><span class="p">:</span>
<span class="k">print</span> <span class="s">'packing the double failed:'</span><span class="p">,</span> <span class="n">instance</span><span class="o">.</span><span class="n">msg</span>
</pre></div>
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<li><a class="reference external" href="#">14.5. <tt class="docutils literal"><span class="pre">xdrlib</span></tt> — Encode and decode XDR data</a><ul>
<li><a class="reference external" href="#packer-objects">14.5.1. Packer Objects</a></li>
<li><a class="reference external" href="#unpacker-objects">14.5.2. Unpacker Objects</a></li>
<li><a class="reference external" href="#exceptions">14.5.3. Exceptions</a></li>
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