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<H3><A NAME="SECTION0051451000000000000000"></A><A NAME="pickle-inst"></A>
<BR>
3.14.5.1 Pickling and unpickling normal class
    instances
</H3>

<P>
When a pickled class instance is unpickled, its <tt class="method">__init__()</tt>
method is normally <em>not</em> invoked.  If it is desirable that the
<tt class="method">__init__()</tt> method be called on unpickling, an old-style class
can define a method <tt class="method">__getinitargs__()</tt>, which should return a
<em>tuple</em> containing the arguments to be passed to the class
constructor (i.e. <tt class="method">__init__()</tt>).  The
<tt class="method">__getinitargs__()</tt> method is called at
pickle time; the tuple it returns is incorporated in the pickle for
the instance.
<a id='l2h-648' xml:id='l2h-648'></a><a id='l2h-650' xml:id='l2h-650'></a>
<P>
<a id='l2h-652' xml:id='l2h-652'></a>
<P>
New-style types can provide a <tt class="method">__getnewargs__()</tt> method that is
used for protocol 2.  Implementing this method is needed if the type
establishes some internal invariants when the instance is created, or
if the memory allocation is affected by the values passed to the
<tt class="method">__new__()</tt> method for the type (as it is for tuples and
strings).  Instances of a new-style type <tt class="class">C</tt> are created using

<P>
<div class="verbatim"><pre><TT>
 obj = C.__new__(C, *<var>args</var>)
 </TT></pre></div>

<P>
where <var>args</var> is the result of calling <tt class="method">__getnewargs__()</tt> on
the original object; if there is no <tt class="method">__getnewargs__()</tt>, an
empty tuple is assumed.

<P>
<a id='l2h-654' xml:id='l2h-654'></a><a id='l2h-656' xml:id='l2h-656'></a>
<P>
Classes can further influence how their instances are pickled; if the
class defines the method <tt class="method">__getstate__()</tt>, it is called and the
return state is pickled as the contents for the instance, instead of
the contents of the instance's dictionary.  If there is no
<tt class="method">__getstate__()</tt> method, the instance's <tt class="member">__dict__</tt> is
pickled.

<P>
Upon unpickling, if the class also defines the method
<tt class="method">__setstate__()</tt>, it is called with the unpickled
state.<A NAME="tex2html18"
  HREF="#foot8816"><SUP>3.6</SUP></A>  If there is no <tt class="method">__setstate__()</tt> method, the
pickled state must be a dictionary and its items are assigned to the
new instance's dictionary.  If a class defines both
<tt class="method">__getstate__()</tt> and <tt class="method">__setstate__()</tt>, the state object
needn't be a dictionary and these methods can do what they
want.<A NAME="tex2html19"
  HREF="#foot8979"><SUP>3.7</SUP></A>
<P>
<div class="warning"><b class="label">Warning:</b>

  For new-style classes, if <tt class="method">__getstate__()</tt> returns a false
  value, the <tt class="method">__setstate__()</tt> method will not be called.
</div>

<P>
<BR><HR><H4>Footnotes</H4>
<DL>
<DT><A NAME="foot8816">...
state.</A><A
 href="pickle-inst.html#tex2html18"><SUP>3.6</SUP></A></DT>
<DD>These methods can also be used to implement copying
class instances.

</DD>
<DT><A NAME="foot8979">...
want.</A><A
 href="pickle-inst.html#tex2html19"><SUP>3.7</SUP></A></DT>
<DD>This protocol is also used by the shallow and deep
copying operations defined in the
<tt class="module"><a href="module-copy.html">copy</a></tt> module.

</DD>
</DL>
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	54
	55	<H3><A NAME="SECTION0051451000000000000000"></A><A NAME="pickle-inst"></A>
	56	<BR>
	57	3.14.5.1 Pickling and unpickling normal class
	58	instances
	59	</H3>
	60
	61	<P>
	62	When a pickled class instance is unpickled, its <tt class="method">__init__()</tt>
	63	method is normally <em>not</em> invoked. If it is desirable that the
	64	<tt class="method">__init__()</tt> method be called on unpickling, an old-style class
65	can define a method <tt class="method">__getinitargs__()</tt>, which should return a
66	<em>tuple</em> containing the arguments to be passed to the class
67	constructor (i.e. <tt class="method">__init__()</tt>). The
68	<tt class="method">__getinitargs__()</tt> method is called at
69	pickle time; the tuple it returns is incorporated in the pickle for
70	the instance.
71	<a id='l2h-648' xml:id='l2h-648'></a><a id='l2h-650' xml:id='l2h-650'></a>
72	<P>
73	<a id='l2h-652' xml:id='l2h-652'></a>
74	<P>
75	New-style types can provide a <tt class="method">__getnewargs__()</tt> method that is
76	used for protocol 2. Implementing this method is needed if the type
77	establishes some internal invariants when the instance is created, or
78	if the memory allocation is affected by the values passed to the
79	<tt class="method">__new__()</tt> method for the type (as it is for tuples and
80	strings). Instances of a new-style type <tt class="class">C</tt> are created using
81
82	<P>
83	<div class="verbatim"><pre><TT>
84	obj = C.__new__(C, *<var>args</var>)
85	</TT></pre></div>
86
87	<P>
88	where <var>args</var> is the result of calling <tt class="method">__getnewargs__()</tt> on
89	the original object; if there is no <tt class="method">__getnewargs__()</tt>, an
90	empty tuple is assumed.
91
92	<P>
93	<a id='l2h-654' xml:id='l2h-654'></a><a id='l2h-656' xml:id='l2h-656'></a>
94	<P>
95	Classes can further influence how their instances are pickled; if the
96	class defines the method <tt class="method">__getstate__()</tt>, it is called and the
97	return state is pickled as the contents for the instance, instead of
98	the contents of the instance's dictionary. If there is no
99	<tt class="method">__getstate__()</tt> method, the instance's <tt class="member">__dict__</tt> is
100	pickled.
101
102	<P>
103	Upon unpickling, if the class also defines the method
104	<tt class="method">__setstate__()</tt>, it is called with the unpickled
105	state.<A NAME="tex2html18"
106	HREF="#foot8816"><SUP>3.6</SUP></A> If there is no <tt class="method">__setstate__()</tt> method, the
107	pickled state must be a dictionary and its items are assigned to the
108	new instance's dictionary. If a class defines both
109	<tt class="method">__getstate__()</tt> and <tt class="method">__setstate__()</tt>, the state object
110	needn't be a dictionary and these methods can do what they
111	want.<A NAME="tex2html19"
112	HREF="#foot8979"><SUP>3.7</SUP></A>
113	<P>
114	<div class="warning"><b class="label">Warning:</b>
115
116	For new-style classes, if <tt class="method">__getstate__()</tt> returns a false
117	value, the <tt class="method">__setstate__()</tt> method will not be called.
118	</div>
119
120	<P>
121	<BR><HR><H4>Footnotes</H4>
122	<DL>
123	<DT><A NAME="foot8816">...
124	state.</A><A
125	href="pickle-inst.html#tex2html18"><SUP>3.6</SUP></A></DT>
126	<DD>These methods can also be used to implement copying
127	class instances.
128
129	</DD>
130	<DT><A NAME="foot8979">...
131	want.</A><A
132	href="pickle-inst.html#tex2html19"><SUP>3.7</SUP></A></DT>
133	<DD>This protocol is also used by the shallow and deep
134	copying operations defined in the
135	<tt class="module"><a href="module-copy.html">copy</a></tt> module.
136
137	</DD>
138	</DL>
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