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<H2><A NAME="SECTION0051420000000000000000">
3.14.2 Data stream format</A>
</H2>

<P>
The data format used by <tt class="module">pickle</tt> is Python-specific.  This has
the advantage that there are no restrictions imposed by external
standards such as XDR<a id='l2h-632' xml:id='l2h-632'></a>
(which can't represent pointer sharing); however it means that
non-Python programs may not be able to reconstruct pickled Python
objects.

<P>
By default, the <tt class="module">pickle</tt> data format uses a printable ASCII
representation.  This is slightly more voluminous than a binary
representation.  The big advantage of using printable ASCII (and of
some other characteristics of <tt class="module">pickle</tt>'s representation) is that
for debugging or recovery purposes it is possible for a human to read
the pickled file with a standard text editor.

<P>
There are currently 3 different protocols which can be used for pickling.

<P>

<UL>
<LI>Protocol version 0 is the original ASCII protocol and is backwards
compatible with earlier versions of Python.

<P>
</LI>
<LI>Protocol version 1 is the old binary format which is also compatible
with earlier versions of Python.

<P>
</LI>
<LI>Protocol version 2 was introduced in Python 2.3.  It provides
much more efficient pickling of new-style classes.

<P>
</LI>
</UL>

<P>
Refer to PEP 307 for more information.

<P>
If a <var>protocol</var> is not specified, protocol 0 is used.
If <var>protocol</var> is specified as a negative value
or <tt class="constant">HIGHEST_PROTOCOL</tt>,
the highest protocol version available will be used.

<P>

<span class="versionnote">Changed in version 2.3:
The <var>bin</var> parameter is deprecated and only provided
for backwards compatibility.  You should use the <var>protocol</var>
parameter instead.</span>

<P>
A binary format, which is slightly more efficient, can be chosen by
specifying a true value for the <var>bin</var> argument to the
<tt class="class">Pickler</tt> constructor or the <tt class="function">dump()</tt> and <tt class="function">dumps()</tt>
functions.  A <var>protocol</var> version &gt;= 1 implies use of a binary format.

<P>

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