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<title>3.14.2 Data stream format
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<H2><A NAME=
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3.14.2 Data stream format
</A>
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-
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(which can't represent pointer sharing); however it means that
non-Python programs may not be able to reconstruct pickled Python
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.
There are currently
3 different protocols which can be used for pickling.
<LI>Protocol version
0 is the original ASCII protocol and is backwards
compatible with earlier versions of Python.
<LI>Protocol version
1 is the old binary format which is also compatible
with earlier versions of Python.
<LI>Protocol version
2 was introduced in Python
2.3. It provides
much more efficient pickling of new-style classes.
Refer to PEP
307 for more information.
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.
<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>
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
>=
1 implies use of a binary format.
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<span class=
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2005.
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