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<title>12.17.1 Packer Objects </title>
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<H2><A NAME="SECTION00141710000000000000000"></A><A NAME="xdr-packer-objects"></A>
<BR>
12.17.1 Packer Objects
</H2>

<P>
<tt class="class">Packer</tt> instances have the following methods:

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4165' xml:id='l2h-4165' class="method">get_buffer</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
Returns the current pack buffer as a string.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4166' xml:id='l2h-4166' class="method">reset</tt></b>(</nobr></td>
  <td><var></var>)</td></tr></table></dt>
<dd>
Resets the pack buffer to the empty string.
</dl>

<P>
In general, you can pack any of the most common XDR data types by
calling the appropriate <code>pack_<var>type</var>()</code> method.  Each method
takes a single argument, the value to pack.  The following simple data
type packing methods are supported: <tt class="method">pack_uint()</tt>,
<tt class="method">pack_int()</tt>, <tt class="method">pack_enum()</tt>, <tt class="method">pack_bool()</tt>,
<tt class="method">pack_uhyper()</tt>, and <tt class="method">pack_hyper()</tt>.

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4167' xml:id='l2h-4167' class="method">pack_float</tt></b>(</nobr></td>
  <td><var>value</var>)</td></tr></table></dt>
<dd>
Packs the single-precision floating point number <var>value</var>.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4168' xml:id='l2h-4168' class="method">pack_double</tt></b>(</nobr></td>
  <td><var>value</var>)</td></tr></table></dt>
<dd>
Packs the double-precision floating point number <var>value</var>.
</dl>

<P>
The following methods support packing strings, bytes, and opaque data:

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4169' xml:id='l2h-4169' class="method">pack_fstring</tt></b>(</nobr></td>
  <td><var>n, s</var>)</td></tr></table></dt>
<dd>
Packs a fixed length string, <var>s</var>.  <var>n</var> 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.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4170' xml:id='l2h-4170' class="method">pack_fopaque</tt></b>(</nobr></td>
  <td><var>n, data</var>)</td></tr></table></dt>
<dd>
Packs a fixed length opaque data stream, similarly to
<tt class="method">pack_fstring()</tt>.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4171' xml:id='l2h-4171' class="method">pack_string</tt></b>(</nobr></td>
  <td><var>s</var>)</td></tr></table></dt>
<dd>
Packs a variable length string, <var>s</var>.  The length of the string is
first packed as an unsigned integer, then the string data is packed
with <tt class="method">pack_fstring()</tt>.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4172' xml:id='l2h-4172' class="method">pack_opaque</tt></b>(</nobr></td>
  <td><var>data</var>)</td></tr></table></dt>
<dd>
Packs a variable length opaque data string, similarly to
<tt class="method">pack_string()</tt>.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4173' xml:id='l2h-4173' class="method">pack_bytes</tt></b>(</nobr></td>
  <td><var>bytes</var>)</td></tr></table></dt>
<dd>
Packs a variable length byte stream, similarly to <tt class="method">pack_string()</tt>.
</dl>

<P>
The following methods support packing arrays and lists:

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4174' xml:id='l2h-4174' class="method">pack_list</tt></b>(</nobr></td>
  <td><var>list, pack_item</var>)</td></tr></table></dt>
<dd>
Packs a <var>list</var> 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 <code>1</code> is packed first, followed by the data value
from the list.  <var>pack_item</var> is the function that is called to pack
the individual item.  At the end of the list, an unsigned integer
<code>0</code> is packed.

<P>
For example, to pack a list of integers, the code might appear like
this:

<P>
<div class="verbatim"><pre>
import xdrlib
p = xdrlib.Packer()
p.pack_list([1, 2, 3], p.pack_int)
</pre></div>
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4175' xml:id='l2h-4175' class="method">pack_farray</tt></b>(</nobr></td>
  <td><var>n, array, pack_item</var>)</td></tr></table></dt>
<dd>
Packs a fixed length list (<var>array</var>) of homogeneous items.  <var>n</var>
is the length of the list; it is <em>not</em> packed into the buffer,
but a <tt class="exception">ValueError</tt> exception is raised if
<code>len(<var>array</var>)</code> is not equal to <var>n</var>.  As above,
<var>pack_item</var> is the function used to pack each element.
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-4176' xml:id='l2h-4176' class="method">pack_array</tt></b>(</nobr></td>
  <td><var>list, pack_item</var>)</td></tr></table></dt>
<dd>
Packs a variable length <var>list</var> of homogeneous items.  First, the
length of the list is packed as an unsigned integer, then each element
is packed as in <tt class="method">pack_farray()</tt> above.
</dl>

<P>

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<span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span>
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