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| 55 | <H2><A NAME="SECTION0051420000000000000000"> |
| 56 | 3.14.2 Data stream format</A> |
| 57 | </H2> |
| 58 | |
| 59 | <P> |
| 60 | The data format used by <tt class="module">pickle</tt> is Python-specific. This has |
| 61 | the advantage that there are no restrictions imposed by external |
| 62 | standards such as XDR<a id='l2h-632' xml:id='l2h-632'></a> |
| 63 | (which can't represent pointer sharing); however it means that |
| 64 | non-Python programs may not be able to reconstruct pickled Python |
| 65 | objects. |
| 66 | |
| 67 | <P> |
| 68 | By default, the <tt class="module">pickle</tt> data format uses a printable ASCII |
| 69 | representation. This is slightly more voluminous than a binary |
| 70 | representation. The big advantage of using printable ASCII (and of |
| 71 | some other characteristics of <tt class="module">pickle</tt>'s representation) is that |
| 72 | for debugging or recovery purposes it is possible for a human to read |
| 73 | the pickled file with a standard text editor. |
| 74 | |
| 75 | <P> |
| 76 | There are currently 3 different protocols which can be used for pickling. |
| 77 | |
| 78 | <P> |
| 79 | |
| 80 | <UL> |
| 81 | <LI>Protocol version 0 is the original ASCII protocol and is backwards |
| 82 | compatible with earlier versions of Python. |
| 83 | |
| 84 | <P> |
| 85 | </LI> |
| 86 | <LI>Protocol version 1 is the old binary format which is also compatible |
| 87 | with earlier versions of Python. |
| 88 | |
| 89 | <P> |
| 90 | </LI> |
| 91 | <LI>Protocol version 2 was introduced in Python 2.3. It provides |
| 92 | much more efficient pickling of new-style classes. |
| 93 | |
| 94 | <P> |
| 95 | </LI> |
| 96 | </UL> |
| 97 | |
| 98 | <P> |
| 99 | Refer to PEP 307 for more information. |
| 100 | |
| 101 | <P> |
| 102 | If a <var>protocol</var> is not specified, protocol 0 is used. |
| 103 | If <var>protocol</var> is specified as a negative value |
| 104 | or <tt class="constant">HIGHEST_PROTOCOL</tt>, |
| 105 | the highest protocol version available will be used. |
| 106 | |
| 107 | <P> |
| 108 | |
| 109 | <span class="versionnote">Changed in version 2.3: |
| 110 | The <var>bin</var> parameter is deprecated and only provided |
| 111 | for backwards compatibility. You should use the <var>protocol</var> |
| 112 | parameter instead.</span> |
| 113 | |
| 114 | <P> |
| 115 | A binary format, which is slightly more efficient, can be chosen by |
| 116 | specifying a true value for the <var>bin</var> argument to the |
| 117 | <tt class="class">Pickler</tt> constructor or the <tt class="function">dump()</tt> and <tt class="function">dumps()</tt> |
| 118 | functions. A <var>protocol</var> version >= 1 implies use of a binary format. |
| 119 | |
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