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<H1><A NAME="SECTION0051900000000000000000">
3.19 <tt class="module">marshal</tt> --
         Internal Python object serialization</A>
</H1>

<P>
<A NAME="module-marshal"></A>

<P>
This module contains functions that can read and write Python
values in a binary format.  The format is specific to Python, but
independent of machine architecture issues (e.g., you can write a
Python value to a file on a PC, transport the file to a Sun, and read
it back there).  Details of the format are undocumented on purpose;
it may change between Python versions (although it rarely
does).<A NAME="tex2html24"
  HREF="#foot9695"><SUP>3.12</SUP></A>
<P>
This is not a general ``persistence'' module.  For general persistence
and transfer of Python objects through RPC calls, see the modules
<tt class="module"><a href="module-pickle.html">pickle</a></tt> and <tt class="module"><a href="module-shelve.html">shelve</a></tt>.  The <tt class="module">marshal</tt> module exists
mainly to support reading and writing the ``pseudo-compiled'' code for
Python modules of <span class="file">.pyc</span> files.  Therefore, the Python
maintainers reserve the right to modify the marshal format in backward
incompatible ways should the need arise.  If you're serializing and
de-serializing Python objects, use the <tt class="module">pickle</tt> module instead.  
<a id='l2h-686' xml:id='l2h-686'></a>
<a id='l2h-680' xml:id='l2h-680'></a>
<P>
<div class="warning"><b class="label">Warning:</b>

The <tt class="module">marshal</tt> module is not intended to be secure against
erroneous or maliciously constructed data.  Never unmarshal data
received from an untrusted or unauthenticated source.
</div>

<P>
Not all Python object types are supported; in general, only objects
whose value is independent from a particular invocation of Python can
be written and read by this module.  The following types are supported:
<code>None</code>, integers, long integers, floating point numbers,
strings, Unicode objects, tuples, lists, dictionaries, and code
objects, where it should be understood that tuples, lists and
dictionaries are only supported as long as the values contained
therein are themselves supported; and recursive lists and dictionaries
should not be written (they will cause infinite loops).

<P>
<strong>Caveat:</strong> On machines where C's <code>long int</code> type has more than
32 bits (such as the DEC Alpha), it is possible to create plain Python
integers that are longer than 32 bits.
If such an integer is marshaled and read back in on a machine where
C's <code>long int</code> type has only 32 bits, a Python long integer object
is returned instead.  While of a different type, the numeric value is
the same.  (This behavior is new in Python 2.2.  In earlier versions,
all but the least-significant 32 bits of the value were lost, and a
warning message was printed.)

<P>
There are functions that read/write files as well as functions
operating on strings.

<P>
The module defines these functions:

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-681' xml:id='l2h-681' class="function">dump</tt></b>(</nobr></td>
  <td><var>value, file</var><big>[</big><var>, version</var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
  Write the value on the open file.  The value must be a supported
  type.  The file must be an open file object such as
  <code>sys.stdout</code> or returned by <tt class="function">open()</tt> or
  <tt class="function">posix.popen()</tt>.  It must be opened in binary mode
  (<code>'wb'</code> or <code>'w+b'</code>).

<P>
If the value has (or contains an object that has) an unsupported type,
  a <tt class="exception">ValueError</tt> exception is raised -- but garbage data
  will also be written to the file.  The object will not be properly
  read back by <tt class="function">load()</tt>.

<P>

<span class="versionnote">New in version 2.4:
The <var>version</var> argument indicates the data
  format that <code>dump</code> should use (see below).</span>

</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-682' xml:id='l2h-682' class="function">load</tt></b>(</nobr></td>
  <td><var>file</var>)</td></tr></table></dt>
<dd>
  Read one value from the open file and return it.  If no valid value
  is read, raise <tt class="exception">EOFError</tt>, <tt class="exception">ValueError</tt> or
  <tt class="exception">TypeError</tt>.  The file must be an open file object opened
  in binary mode (<code>'rb'</code> or <code>'r+b'</code>).

<P>
<span class="warning"><b class="label">Warning:</b>
If an object containing an unsupported type was
  marshalled with <tt class="function">dump()</tt>, <tt class="function">load()</tt> will substitute
  <code>None</code> for the unmarshallable type.</span>
</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-683' xml:id='l2h-683' class="function">dumps</tt></b>(</nobr></td>
  <td><var>value</var><big>[</big><var>, version</var><big>]</big><var></var>)</td></tr></table></dt>
<dd>
  Return the string that would be written to a file by
  <code>dump(<var>value</var>, <var>file</var>)</code>.  The value must be a supported
  type.  Raise a <tt class="exception">ValueError</tt> exception if value has (or
  contains an object that has) an unsupported type.

<P>

<span class="versionnote">New in version 2.4:
The <var>version</var> argument indicates the data
  format that <code>dumps</code> should use (see below).</span>

</dl>

<P>
<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
  <td><nobr><b><tt id='l2h-684' xml:id='l2h-684' class="function">loads</tt></b>(</nobr></td>
  <td><var>string</var>)</td></tr></table></dt>
<dd>
  Convert the string to a value.  If no valid value is found, raise
  <tt class="exception">EOFError</tt>, <tt class="exception">ValueError</tt> or
  <tt class="exception">TypeError</tt>.  Extra characters in the string are ignored.
</dl>

<P>
In addition, the following constants are defined:

<P>
<dl><dt><b><tt id='l2h-685' xml:id='l2h-685'>version</tt></b></dt>
<dd>
  Indicates the format that the module uses. Version 0 is the
  historical format, version 1 (added in Python 2.4) shares
  interned strings. The current version is 1.

<P>

<span class="versionnote">New in version 2.4.</span>

</dd></dl>
<BR><HR><H4>Footnotes</H4>
<DL>
<DT><A NAME="foot9695">...
does).</A><A
 href="module-marshal.html#tex2html24"><SUP>3.12</SUP></A></DT>
<DD>The name of this module stems from a bit of
  terminology used by the designers of Modula-3 (amongst others), who
  use the term ``marshalling'' for shipping of data around in a
  self-contained form. Strictly speaking, ``to marshal'' means to
  convert some data from internal to external form (in an RPC buffer for
  instance) and ``unmarshalling'' for the reverse process.

</DD>
</DL>
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	54
	55	<H1><A NAME="SECTION0051900000000000000000">
	56	3.19 <tt class="module">marshal</tt> --
	57	Internal Python object serialization</A>
	58	</H1>
	59
	60	<P>
	61	<A NAME="module-marshal"></A>
	62
	63	<P>
	64	This module contains functions that can read and write Python
65	values in a binary format. The format is specific to Python, but
66	independent of machine architecture issues (e.g., you can write a
67	Python value to a file on a PC, transport the file to a Sun, and read
68	it back there). Details of the format are undocumented on purpose;
69	it may change between Python versions (although it rarely
70	does).<A NAME="tex2html24"
71	HREF="#foot9695"><SUP>3.12</SUP></A>
72	<P>
73	This is not a general ``persistence'' module. For general persistence
74	and transfer of Python objects through RPC calls, see the modules
75	<tt class="module"><a href="module-pickle.html">pickle</a></tt> and <tt class="module"><a href="module-shelve.html">shelve</a></tt>. The <tt class="module">marshal</tt> module exists
76	mainly to support reading and writing the ``pseudo-compiled'' code for
77	Python modules of <span class="file">.pyc</span> files. Therefore, the Python
78	maintainers reserve the right to modify the marshal format in backward
79	incompatible ways should the need arise. If you're serializing and
80	de-serializing Python objects, use the <tt class="module">pickle</tt> module instead.
81	<a id='l2h-686' xml:id='l2h-686'></a>
82	<a id='l2h-680' xml:id='l2h-680'></a>
83	<P>
84	<div class="warning"><b class="label">Warning:</b>
85
86	The <tt class="module">marshal</tt> module is not intended to be secure against
87	erroneous or maliciously constructed data. Never unmarshal data
88	received from an untrusted or unauthenticated source.
89	</div>
90
91	<P>
92	Not all Python object types are supported; in general, only objects
93	whose value is independent from a particular invocation of Python can
94	be written and read by this module. The following types are supported:
95	<code>None</code>, integers, long integers, floating point numbers,
96	strings, Unicode objects, tuples, lists, dictionaries, and code
97	objects, where it should be understood that tuples, lists and
98	dictionaries are only supported as long as the values contained
99	therein are themselves supported; and recursive lists and dictionaries
100	should not be written (they will cause infinite loops).
101
102	<P>
103	<strong>Caveat:</strong> On machines where C's <code>long int</code> type has more than
104	32 bits (such as the DEC Alpha), it is possible to create plain Python
105	integers that are longer than 32 bits.
106	If such an integer is marshaled and read back in on a machine where
107	C's <code>long int</code> type has only 32 bits, a Python long integer object
108	is returned instead. While of a different type, the numeric value is
109	the same. (This behavior is new in Python 2.2. In earlier versions,
110	all but the least-significant 32 bits of the value were lost, and a
111	warning message was printed.)
112
113	<P>
114	There are functions that read/write files as well as functions
115	operating on strings.
116
117	<P>
118	The module defines these functions:
119
120	<P>
121	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
122	<td><nobr><b><tt id='l2h-681' xml:id='l2h-681' class="function">dump</tt></b>(</nobr></td>
123	<td><var>value, file</var><big>[</big><var>, version</var><big>]</big><var></var>)</td></tr></table></dt>
124	<dd>
125	Write the value on the open file. The value must be a supported
126	type. The file must be an open file object such as
127	<code>sys.stdout</code> or returned by <tt class="function">open()</tt> or
128	<tt class="function">posix.popen()</tt>. It must be opened in binary mode
129	(<code>'wb'</code> or <code>'w+b'</code>).
130
131	<P>
132	If the value has (or contains an object that has) an unsupported type,
133	a <tt class="exception">ValueError</tt> exception is raised -- but garbage data
134	will also be written to the file. The object will not be properly
135	read back by <tt class="function">load()</tt>.
136
137	<P>
138
139	<span class="versionnote">New in version 2.4:
140	The <var>version</var> argument indicates the data
141	format that <code>dump</code> should use (see below).</span>
142
143	</dl>
144
145	<P>
146	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
147	<td><nobr><b><tt id='l2h-682' xml:id='l2h-682' class="function">load</tt></b>(</nobr></td>
148	<td><var>file</var>)</td></tr></table></dt>
149	<dd>
150	Read one value from the open file and return it. If no valid value
151	is read, raise <tt class="exception">EOFError</tt>, <tt class="exception">ValueError</tt> or
152	<tt class="exception">TypeError</tt>. The file must be an open file object opened
153	in binary mode (<code>'rb'</code> or <code>'r+b'</code>).
154
155	<P>
156	<span class="warning"><b class="label">Warning:</b>
157	If an object containing an unsupported type was
158	marshalled with <tt class="function">dump()</tt>, <tt class="function">load()</tt> will substitute
159	<code>None</code> for the unmarshallable type.</span>
160	</dl>
161
162	<P>
163	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
164	<td><nobr><b><tt id='l2h-683' xml:id='l2h-683' class="function">dumps</tt></b>(</nobr></td>
165	<td><var>value</var><big>[</big><var>, version</var><big>]</big><var></var>)</td></tr></table></dt>
166	<dd>
167	Return the string that would be written to a file by
168	<code>dump(<var>value</var>, <var>file</var>)</code>. The value must be a supported
169	type. Raise a <tt class="exception">ValueError</tt> exception if value has (or
170	contains an object that has) an unsupported type.
171
172	<P>
173
174	<span class="versionnote">New in version 2.4:
175	The <var>version</var> argument indicates the data
176	format that <code>dumps</code> should use (see below).</span>
177
178	</dl>
179
180	<P>
181	<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline">
182	<td><nobr><b><tt id='l2h-684' xml:id='l2h-684' class="function">loads</tt></b>(</nobr></td>
183	<td><var>string</var>)</td></tr></table></dt>
184	<dd>
185	Convert the string to a value. If no valid value is found, raise
186	<tt class="exception">EOFError</tt>, <tt class="exception">ValueError</tt> or
187	<tt class="exception">TypeError</tt>. Extra characters in the string are ignored.
188	</dl>
189
190	<P>
191	In addition, the following constants are defined:
192
193	<P>
194	<dl><dt><b><tt id='l2h-685' xml:id='l2h-685'>version</tt></b></dt>
195	<dd>
196	Indicates the format that the module uses. Version 0 is the
197	historical format, version 1 (added in Python 2.4) shares
198	interned strings. The current version is 1.
199
200	<P>
201
202	<span class="versionnote">New in version 2.4.</span>
203
204	</dd></dl>
205	<BR><HR><H4>Footnotes</H4>
206	<DL>
207	<DT><A NAME="foot9695">...
208	does).</A><A
209	href="module-marshal.html#tex2html24"><SUP>3.12</SUP></A></DT>
210	<DD>The name of this module stems from a bit of
211	terminology used by the designers of Modula-3 (amongst others), who
212	use the term ``marshalling'' for shipping of data around in a
213	self-contained form. Strictly speaking, ``to marshal'' means to
214	convert some data from internal to external form (in an RPC buffer for
215	instance) and ``unmarshalling'' for the reverse process.
216
217	</DD>
218	</DL>
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